|“||Riko…I'm going with you…to the bottom of the Abyss.||”|
Reg is a robotic being who appears to be a little boy. His actual age, origins, and even name are unknown because he cannot recall anything about his life before his encounter with Riko. He is named after a dog Riko used to have.
Due to design similarities, Gaburoon wondered if Reg and they might share the same creator; noting that Interference Units don't cross layers and them having no data regarding Interference Units of Reg's kind.
Reg has light brown skin and dark hair. He wears a metal helmet with two asymmetrical horns protruding out of the sides and what appears to be a glass lens in the front, which, according to Nanachi's theory, displays the number of Incinerator charges he has left to use.
Underneath his helmet is a jagged metal headband of some sort, with bolts on either side keeping it in place on his head. His ears are slightly pointed. Reg's eyes are yellow, and his pupils are catlike, vertical slits. There are two red patches of skin on his cheeks, and four more on either side of his rib cage. His eyebrows are small and gray. Though he is a robot, the only parts of him that appear to be mechanical are his arms and legs, which are bulky compared to the rest of his body. He has nipples, a belly button, and even human genitals.
He is usually shirtless, save for the tattered red cape he is wearing when Riko finds him. His washed-out green and purple pants are baggy and stop just below his knees. The buckle of his belt resembles an eye with a long slit. In the events transpiring at the Ido Front, Reg loses his right forearm while Umbra Hands run tests on him and earns a scar on his belly button after his fight with Bondrewd.
In an encounter with a Turbinid-Dragon, in which he blocks a strike from the creature, Reg's remaining left arm gets chipped leaving a small scratch on his left forearm. He is later equipped with the Artifact Gentle Knock which is attached in place of his right forearm.
Despite being a formidable fighter, Reg is rather shy, naive, and unassertive. He blushes easily and often cries when in distress. However, when forced into danger or an unpleasant situation, he is shown to be hot-tempered and sharp, compared to Riko's analytic, noncombatant role. Regardless of his skittishness, Reg has made it his sworn duty to protect Riko and doesn't hesitate to put up a fight when she is in harm's way.
Very little is known of Reg's past, as he remembers nothing before meeting Riko. Reg is found by Riko in the Abode of Fossils at a depth of 100–220 meters after he used his incinerator to save Riko's life.
He and Riko presume he is from the bottom of the Abyss, as one of Lyza's sketches depicts a human-like silhouette from the pit that heavily resembles him. According to Lyza's notes, she first encountered the creature around the 7th layer.
As he descends further into the Abyss, Reg's memories come back in little snippets at a time. He eventually recalls that at some point he had met Lyza, though he does not remember any specific details about her.
Reg met Faputa and Gaburoon shorty after the latter had been damaged by a Turbinid-Dragon. Faputa was at first wary of him, but as they spent time together they grew closer to each other and Reg gifted Faputa the googles he wore on his helmet at the time as a sign of friendship. Reg also protected Gaburoon until he was fully functional again. Before Reg left the 6th layer, he promised to Faputa to come back to settle the score of her fate and wanted to go onto an adventure with her afterwards.
While collecting Artifacts in the Abyss's 1st layer, Riko is being chased by a Crimson Splitjaw. When a beam of energy hits the Splitjaw and chases it away, a curious Riko follows the wreckage from the beam to its source, where she finds an unconscious robot boy. Upon further inspection, Riko realizes he is not human, and with the help of Nat, she brings him out of the Abyss and back to Belchero Orphanage. There she studies and takes notes on Reg's body and is able to wake him up using a jolt of electricity. She names the robot Reg after a dog she used to own, helps him settle in at the orphanage, and tells him about Orth and the Abyss.
During the Resurrection Festival, a celebration in honor of the death of a White Whistle Delver in the Abyss, Hablog returns from the Abyss with Riko's mother's White Whistle along with some of Lyza's field notes. While Riko and Reg look through them, they notice one of them contains a sketch of a figure that looks similar to Reg, along with a letter that states that Lyza is waiting for her daughter at the bottom of the Abyss. Riko decides to leave Orth and go to the bottom of the Abyss, and Reg decides to go with her. Before leaving, Reg visits Kiyui in his room to say goodbye and warn him not to look in the mirror on his birthday. Then he and Riko leave the orphanage in the middle of the night with Nat and Shiggy to see them off. When they reach the Wharf district, a part of Orth that dips into the Abyss, Riko and Reg say their final goodbyes to Nat and Shiggy, and begin their descent towards the bottom of the world.
Descent to the Abyss Arc
After the sad goodbyes from Riko and Reg to Nat and Shiggy, they finally descend and land somewhere in the first layer of the Abyss, with a depth of 820 meters. While they are eating their breakfast, Riko notices Jiruo stuck a red slip with the contents of Lyza's sealed letter and the message, "I'll depart at dawn to capture you", into their belongings: Riko rushes and packs their things with Reg's help, and they leave the premises post-haste.
Immediately afterwards, they land in a Silkfang's territory and are ambushed by it; however, they escape while defending themselves. They witness the 2nd layer for the first time. Reg suddenly hears his own voice—something about his past–and later, he accompanies Riko for a short break. While they are having a conversation, Reg sees a Delver above some boulders who chases them while they rush to escape and hide—Reg defends Riko. Not very much later, the delver catches up—and is revealed to be the Black Whistle Delver Hablog, who was impressed by the group's fast pace. Hablog's main objective was to meet and inspect Reg, because Nat and Shiggy told him about Reg's true nature. Instead of taking them back to Orth, he offers to escort them to the Seeker Camp, which Riko declines. He then gives Riko a warning about Ozen, some medicine, and other supplies and lets them go.
Shortly after they arrive on the 2nd layer, Riko and Reg hear a cry for help, but it is one of a Corpse-Weeper, which mimics its victims cries of pain and fear: they follow it. While observing the Corpse-Weeper, they are ambushed by a colony of them, and one of them snatches Riko. She struggles initially, but she loses consciousness due to the strain of ascension. Reg, unsure of what to do, recalls his memory of using the Incinerator to save Riko from the Crimson Splitjaw in the 1st layer. Instinctively, he raises his arm and fires his Incinerator, obliterating the colony of Corpse-Weepers and saving Riko from being fed to the Corpse-Weeper's young.
Seeker Camp Arc
After a short climb down the top of the 2nd layer, Reg and Riko find themselves in the company of the Immovable Lord, Ozen, at the Seeker Camp; her domain is to supervise descent past the 2nd layer. While in the presence of Ozen; Riko and Reg make friends with Marulk, Ozen's pupil and servant. Later on, Riko learns from Ozen about her birth in the Abyss and that she was a stillborn that only survived due to the Curse-Warding Box.
Ozen continues to agonize Riko by assuming she probably also will stop moving at some point. Hearing that, Regs steps in and tells Ozen that she has gone too far and a fight erupts between them, one-sidedly in Ozen's favor, Reg arrives at the conclusion that only a shot from his Incinerator will be able to beat Ozen. He tries but misses his shot. Ozen stomps him until he fells unconscious as Riko can do nothing but helplessly watch.
During the time Reg is unconscious, Marulk had panicked and went to get the other Subterranean Bandits to stop the fight. Afterward, it's revealed that Ozen was trying to provoke Reg and Riko into a fight in order to test if they are ready to make their way further down The Abyss. She tells them that Riko's lack of communication in battle, as well as Reg's lack of being able to judge the right timing to use his Incinerator are fatal flaws that would have them wind up dead sooner or later. Furthermore, because Reg falls unconscious within ten minutes after using his Incinerator, Riko needs to be able to protect herself. As such, she instructs both of them to stay ten days in the forest behind the Seeker Camp as survival training.
During their survival training Riko and Reg learn to be more adapt and aware of their strengths and weaknesses. Reg and Riko return to the Seeker Camp after ten days and Marulk congratulates them on passing as most people don't even manage to make it even a week. Ozen tells Reg and Riko that the training camp also should have helped both of them to train to keep track on time due to The Abyss causing a person's sense of time to get lost. Ozen also tells them about the secrets transmitted from the Last Dives of generations of White Whistle Delvers, which are only passed down via word of mouth by none but themselves, and teaches them how to use Blaze Reap as a replacement for the Incinerator. Afterwards, Riko and Reg leave the Seeker Camp to advance down to the 3rd layer.
The Great Fault Arc
Riko and Reg descend through the 3rd layer, the Great Fault, which features a long, vertical shaft. The trip is made more dangerous by the Madokajack constantly seeking prey. Fortunately, there are plenty of Neritantan who make nests in holes along the shaft. Riko uses them as distractions to draw the predators away. Riko and Reg run into the very same Crimson Splitjaw that Reg saved Riko from previously. Reg recalls Ozen's warning: using the Incinerator causes Reg to fall asleep within ten minutes, and for two hours afterward, it is impossible to wake him up. This would leave Riko completely unprotected, so if Reg uses the Incinerator, he must make absolutely sure that he defeats the threat before him. Riko recalls that the Crimson Splitjaw eats Artifacts, so she throws one to distract it, allowing Reg to attack from below. He knocks the Crimson Splitjaw into the shaft, where it is attacked by several Madokajack.
Poison and Soul Liberation Arc
During Riko's and Reg's descent to the 4th layer they are attacked by an Orb Piercer. During the battle Riko's hand gets stabbed by one of the Orb Piercer's venomous needles, causing her to fall under the affects of its venom and, in combination with the curse due to ascending to fast in retreat, starts to hallucinate and bleeding out of every hole in her body. Shortly afterward she loses consciousness leaving Reg in despair.
Nanachi reveals themself to Reg, due to seeing him crying over Riko's body. Because the two's relationship reminds Nanachi of their relationship with Mitty, Nanachi decides to aid them. With Nanachi's help Reg starts to gather the ingredients needed to cure Riko. Afterwards, Nanachi explains to Reg what the Curse of the Abyss is and how it works. Then, after asking Reg to listen to them no matter what, she makes him fight against the Orb Piercer again and, thanks to the help of Nanachi via a communicator, is able to ward it off with a shot from his Incinerator. Nanachi, surprised by the power of it and similarity to Bondrewd's Sparagmos, asks Reg to kill Mitty with it to end her suffering.
Reg, though conflicted, follows Nanachi's wish and comforts them afterwards as they break down in tears due to setting Mitty free, but also losing her. After Riko recovered, Nanachi decides to join Riko and Reg on their journey to the bottom of the Abyss.
Ido Front Arc
After preparations, the group embarks from Nanachi's hideout, reaching the field of Eternal Fortunes. There they encounter one of Bondrewd's Umbra Hands. A brief exchange follows, in which the Umbra Hand tells them that Bondrewd is expecting them. Then, the three of them reach Bondrewd's base, Ido Front.
A girl, Prushka, approaches them and asks if they are her father's guests. A few moments later Bondrewd arrives, greets the trio and informs them that entrance into the 6th layer is only possible with a personalized White Whistle.
He invites them to stay a night and Prushka gives them a tour of the base. During the night, Reg is taken away by the Umbra Hands and they start running tests on him. They even cut off his arm to further analyse it.
Nanachi, Riko, and Prushka find him due to hearing his screams in the hall. Prushka orders the Umbra Hands to stop treating her father's guests that way, only to be informed by them that this area is off limits for her. The trio, together with Prushka, escapes outside the Ido Front and tries to escape in a boat. Only Prushka stays back because she wants to convince Bondrewd to return Reg's arm.
Riko is visibly distraught and cries about the suffering put upon Reg by the Umbra Hands. Reg, lying injured, mentions he can smell the burnt parts of Netherworld Stew. Riko extrapolates from this and other signs (including her mother's notes) that they are located near a Stingerhead nest; the trio uses this to create a trap for Bondrewd.
Shortly afterwards, Reg, Nanachi, and Riko are confronted by Bondrewd and his Umbra Hands again, however they have been led into a trap by the trio and are attacked by Stingerheads. Only Bondrewd survives the attack with his Sparagmos, but is taken care of by a clever strategy of Nanachi and Reg resulting in him being shot by an arrow containing Amaranthine-Deceptor larvae fired by Riko, exposed to the curse, as well crushed by Reg with a boulder. Prushka, who had observed with an Umbra Hand, bursts out in tears over the state Bondrewd is in. The Umbra Hand quickly takes Bondrewd's whistle, as well as removes helment and replaces it with his own, leading him to turn into Bondrewd in the process.
Bondrewd makes the relieved Prushka pass out and reveals to the trio that all Umbra Hands are copies of him he can transfer his consciousness into. After a quick beatdown he leaves them and invites them back to the Ido Front whenever they are ready. Riko notes that Bondrewd maybe uses the artifact, Zoaholic, to transfer parts of his consciousness. Together with Reg the both make a strategy in order to destroy it.
As they sneak back into Ido Front, Nanachi and Riko make their way into what Nanachi calls the processing room while Reg searches for the power plant to destroy it. During that, he is seemingly overloaded and goes out of control. He makes his way back into Ido Front and interrupts the conversation between Bondrewd, Nanachi and Riko by attacking Bondrewd.
A fight between Reg and Bondrewd breaks out. The out of control Reg blasts his Incinerator without consideration for the surroundings, but Bondrewd is able to keep up with him. Only due to Nanachi's interruption, due to not wanting to see Reg in such a state and begging him to stop with a hug, the fight comes to a momentarily halt; with Reg turning back to his usual self.
During the second stage of the fight, Bondrewd reveals that he turned Prushka into a cartridge. This revelation causes Riko to be shaken up to tears because Prushka was a good friend to her and enrages Reg. After Bondrewd's defeat, resulting him to be cut in half, Riko holds Prushka's cartridge close to her and cries. In that moment a stone, like one needed to craft a personal White Whistle, comes out of the cartridge.
Nanachi tells Riko that Prushka most likely assumed the form of the stone to be able to travel along with Riko, which relieves Riko abit. Nanachi makes a harness so Riko can wear Prushka's stone around her neck. As the group gets ready to traverse into the 6th layer, it is shown that Bondrewd's consciousness still lives on within his Umbra Hands as they come to see Riko's group off.
Riko's group uses the altar connecting the 5th to the 6th layer. On their way down, they see various creatures. After leaving the elevator, they decide to make a camp for the night. Nanachi awakens and notices something invaded the camp after they had fallen asleep and stole Prushka's stone. With the help of Meinya, they track it down to a village.
Upon entering the village, a Narehate greets them and introduces themself as Majikaja. Majikaja leads them to jeweler, who is working Prushka's stone to make it into its finalized form. While they are waiting, Majikaja explains a few things about the village, Ilblu, and brings them to a market.
Due to an accident, Meinya is injured by a very curious Narehate and the group witnesses the village's ritual to balance value. In the ritual, the Narehate at fault for Meinya being hurt gets stripped off their belongings and even parts of their skin.
They manage to stay at a inn, but shortly afterwards, an impact causes a shockwave to travel through the village. Majikaja explains it was caused by Faputa; a Narehate praised as embodiment of value. Reg wants to investigate, while Nanachi and Riko stay behind.
As Reg makes his way and steps outside the village, he meets the Narehate praised as "princess" by the villagers, Faputa, and her guardian, Gaburoon. Faputa is quick to approach Reg without hesitation, seemingly having known him before he lost his memories. Upon finding out he forgot her she is shaken and takes him away to further examine him. 
A brief exchange between them follows, in which Faputa insists that Reg's name always has been Reg, but Reg refuses to accept that; saying that he is Reg because Riko gave him that name. He leaves her and starts making his way back to the village. During is way back he is assaulted by a Turbinid-Dragon but Gaburoon rescues him.
The two have a short chat and Gaburoon tells Reg that he could be an Interference Unit similar to themself. Afterwards, Reg continues to make his way back to the village and, upon suddenly hearing Riko's whistle, dashes to her side to protect her from the Fuzosheppu. As he lunges at the creature, it collapses and Wazukyan shows up telling Riko and Reg that the Fuzosheppu is already dead and explains the nature of it. Riko asks him if he knows of a way to get enough value to buy back Nanachi from Belaf. Wazukayn tells them that if they had a body part of Faputa it might be possible and Reg decides to go ask her.
After making his way back to Faputa Reg tells her about the situation with his friend Nanachi and asks her for help. Faputa agrees to give Reg a part of her if he keeps his promise. Uppon asking for more information on the promise between them Faputa rips one of her ears and arms off, happily handing them to Reg telling him "Let's eradicate them together, Reg."
Reg, taken aback by her request, asks what she means by that and Faputa specifies she wants him to be her "helper", because she knows Reg is too kind to destroy the village. In the past, Reg told her his incinerator has the power to "rewrite" the laws stopping Faputa from entering the village and as such she wants him to do so in return for her body parts. Reg and Faputa start making their way back to the village, but because creatures are attracted by the smell of her blood, Gaburoon stays behind to fend them off.
As they arrive at the entrance of the village, Riko comes to greet Reg and catches a glimpse of Faputa. Immediately after Reg steps inside the barrier with Faputa's body parts, the village reacts similar to the Ilblu Balancing, but far stronger and more uncontrolled.
Reg panics and contemplates to bring the parts to Belaf right away, but is stopped by Vueko because she assumes seeing them could drive Belaf insane. When Vueko asks Reg how he acquired the parts, Reg tells her Faputa gave them to him so that he would fulfill his promise. Wazukyan, who had eavesdropped the conversation, concludes Reg must have been "The Prince" and is surprised Reg managed to secure parts of "The Princess". He also casually greets Vueko, expresses his joy of her finally being able to leave her pit, and asks her if she already told them about "The Princess". Vueko reluctantly confirms she has, but notes she told the story from her point of view.
After the conversation between Wazukyan, Riko and the villagers, Juroimoh shows up and starts attacking. Wazukyan quickly grabs Vueko and moves to a higher position to avoid Juroimoh. Reg manages to draw Juroimoh's attention and a fight erupts between them, which leads to Juroimoh transforming into a even more monstrous form with the dark gooey liquid masses.
After his transformation, Juroimoh continues his attack by compressing the gooey liquid masses, and firing them in Reg's direction. Reg contemplates using the part of Faputa he still holds to trick Juroimoh into stealing it, and thus triggering the Ilblu Summoning.
However, Vueko notices his plan, and shouts at him not to try it because Juroimoh is unaffected by it. As Reg is thinking of another way, Juroimoh creates a thin membrane with the gooey liquid masses and flings it towards Reg. Reg manages to pull himself out, but, because of the size, villagers and Riko also get caught up in the membrane.
Without much time to think, Reg decides the best solution is to fire his incinerator and rips away the membrane as well as parts of Juroimoh. However, his blast also opens up an opening in the village. Afterwards, he starts panicking because soon Faputa will arrive and the situation will likely turn into a worst case scenario. Reg asks Moogie, Majikaja and Maaa to protect Riko while he is unconscious, and gives them the part of Faputa as payment.
Shortly afterwards, Faputa arrives. Juroimoh roars at her, but is quickly hit by a shot fired by Gaburoon. Faputa tells the onlooking villagers she will not forgive their sins and the time for their "extermination" has come.
Reg wakes up, after having passed out due to his incinerator, from a loud shriek. Riko, glad that he finally woke up, tells him Gaburoon has protected them while Reg was unconscious. Reg thanks Gaburoon, but is also informed by them that this situation happened due to Reg's resolve. Riko pulls Reg up and asks him to do something about the current situation. As Reg sees the aftermath from the battle between Faputa and the villagers, he is stunned.
All villagers fighting Faputa seem to have been torn apart and lie in piles to her feet, with Faputa still busy tearing the corpses apart.
Faputa continues her one sided battle against the villagers, easily ripping through them. After seeing Riko conflicted and not wanting the things the villagers hold dear to be destroyed, Reg decides to try to confront Faputa. He approaches her and requests her to stop by siding that one of his friends is still in the village, but Faputa tells him she will not stop. She also remarks that he shouldn't try to use his friend as an excuse just so that he wouldn't hurt her feelings and say clearly what he wants to express.
Reg tells her that he will stop her and Faputa tells him she will make him remember what he has to do, even if it means fighting him to do so.
In the battle between Reg and Faputa, in which Faputa tries to make Reg remember his past with her. Reg remarks Faputa should express herself better which shocks Faputa as Reg was the one from whom she learned to express herself in the delver language.
After an exchange of blows, Reg instructs Riko to blow her whistle. This triggers an activation in Reg resulting in him emitting a white glow with enhanced speed. Faputa curses at Riko for using Prushka against her and reveals it was her who instructed Gaburoon to bring the stone into the village. It was in order to test if the bond between Riko and Prushka was truely genuine as well as in hope of bringing Reg to the village because she thought it would trigger his memories to come back.
Reg manages to gain the upper hand, but torn by snippets of memories from his past comming back, he tells Faputa in tears if she keeps following her current path she will keep burning herself until she eventually burns herself out and asks her how he can stop her from doing so.
As his tears fall on Faputa's face she remarks how kind hearted he is, but also a fool, and powerfully slams him down on the ground.
After Reg lost consciousness, Faputa instructs Juroimoh to hold Reg down so that he can't interfere if he wakes up.
Nanachi collected Reg at one point and they are both later seen with Riko's group who escaped the battle scene and the trio apologizes to each other since they all think they made huge mistakes.
Later on after they found Wazukyan and talk to him, Reg holds himself back a little because what Wazukyan says is true but annoys him regardless.
After Wazukyan faded away, they hear sounds in the distance and Majikaja and the other villagers inform them that it is Faputa, calling to them for the first time.
The group ultimately decides to move onward following Faputa's roars.
When Faputa prepares to engage the Turbinid-Dragons again, Reg joins the scene and after a short conversation with him telling her he has not come to get in her way and will take over the battle from here, gets a whiste charge from Riko and starts battling the dragons.
Reg, who manages to drag the creatures outside, notices that when Wazukyan gave up most of his body to the village it also enlargend the bridge leading to its entrance. This gave the creatures an easier way to quickly invade the village. Reg begins extending his arm and swinging it around and creates enough momentum to ultimately destroy the bridge.
When the village collapsed Reg and Majikaja defended the group from the falling debris. After the death of Vueko, Reg asks Faputa to come along with them but she retorts by saying that he can't even rember their promise. Reg saddened says that even after all this time he can't remember and feels bad for it to which Faputa gets frustrated and says it means that she basically has no relation with Reg anymore. Reg counters this by retorically asking her if is former self ever saw this mopey side of Faputa. He continues on with expressing his current self has seen how scray she was, her pain and her beauty and that he wants to gone on an adventure together with her. 
After a brief exchange over Faputa's relief of Reg showing this level of determination for her, she then turns her attention to Riko, telling her that Prushka is saying Riko's role was caring about the people she met.
When their exchange comes to an end, Faputa decides to head off on her own and Reg questions her if she won't come with them. She replies that she will think about it before holding on one last time to Reg's head and afterwards begins to head away onto her own path.
Beyond the village
The trio of Reg, Nanachi and Riko make their way further into the dephts of the 6th layer. As they continue onwards, Reg wonders about Faputa's current whereabouts and hopes she is alright. Nanachi, while continuing their path, points out Faputa had been born in the 6th layer and even managed to stand up to the creatures that attacked the village.
Riko notes that they haven't documented all the locations they had been to so far and thus starts naming them. Reg points out, because she named two similar clocktowers with "last" in their description, it could become a problem in naming pattern if they encounter more similar locations. Riko brushes that thought aside and upon seeing a field of Eternal Fortunes the group is reminded of the Amaranthine-Deceptors which ultimately leads into Nanachi pointing out that they could encounter the other two White Whistle Delvers besides Lyza sooner or later. 
As their conversation shifts onto Faputa again, Nanachi notices that Faputa is following them. Riko calls out to her and asks her if she would like to join them for dinner. 
Faputa slowly apporaches them, climbs onto Reg's head and warps his cape around her. After a brief exchange, Riko asks Faputa if she can understand Lyza's White Whistle as she had shown to be able to communicate with Prushka, too. 
As Riko holds up the whistle to Faputa, Faputa suddenly rises up seemingly in shock. Riko, surprised by that, asks her whats wrong and Faputa seems surprised by what the Whistle is trying to communicate. She then tells them the name of the Whistle is Doni and relays their message of someone waiting at the Pivotal Ring. Riko asks if it could be her mother but Doni clearifys it is not Lyza but someone related to Reg before stating they won't say more on the matter and going sielent.
After concluding the Pivotal Ring must be the ring of light Ozen had mentined, Riko praises Faputa which ultimately leads into her being interested in Faputa's rear atonomy and Faputa allowing her to sniff her rear and Riko expressing how it smells like the sun and something left out to dry.
The group continues onward, collects materials, and also tries to make sense of the Lyza note Moogie had given to Riko during the village incident. Afterwards, Reg and Faputa are tasked with trying to hunt a creature, the Kamazuno. They manage to get a leg of the creature and make a stew with it. Faputa is at first scepitcal of the dish but happily eats it after having a first taste.Riko asks if the food is good and Faputa happily smiles telling her she is not sure yet and wants another bowl.
While the group is asleep during their travels, Reg wakes up Riko to tell her something. Reg tells Riko about the name tags he witnessed falling down and how it most likely relates to something going on in Orth. As Nanachi awakes too, they state it most likely has to do with the time difference to the surface and hence why so many tags fell at once and explain again how the timeflow is different in the lower layers.
Reg notes he hopes the others in the upper layers are alright and Riko gives the rest of the group a motivating speech that most likely White Whistles and ranks close to White Whistle level are aware of the ongoings and will do something about it. During their further travel, Meinya suddenly reacts to something and looks for it. As the group follows Meinya they come upon the corpse of a Black Whistle Delver. 
Reg initally panicks but Nanachi quickly informs him that the Delver is already dead. As the group wonders about his cause of death, and which group he could have belonged to, Nanachi searches him for useful common Artifacts Delvers often carry and they collcet an all-purpose lockpick, Gentle Knock, and an air dumpling, Maama Intobaap from the corpse.
As the group continues their travel, they come upon a herd of Emperorshells and Nanachi, amazed by it, recites lyrics of a folk song| based on the White Whistles they used to read to Mitty. As Nanachi gets sentimental, Faputa reassures them in their bond to Mitty.
The Curse Fleet Arc
Riko's group travels further into the 6th layer with Reg now having one of the Artifacts they recovered from Cravali's corpse attached to his cut-off arm. Nanachi notes it to be Gentle Knock and Artifact one can control with one's mind. After a short exchange between the group of how Reg's arm in Riko's possession can be used to remotely touch Nanachi, notices that the force field has clamed down greatly in the area they are apporaching and this stemming from no more small creatures being present at all ahead. 
As such, they conclude somebody might have set up a trap ahead which excites Riko of the possiblity of someone besides them being out there.
As the group tries to trigger a potential trap by throwing stones in its possible general placement, Nanachi arrives at the conclusion that it would be easier for Reg to just check it out as his ridiculess toughness and stamina most likely would keep him safe. As Reg tries to set off a trap, it is triggered and causes the release of a gas that smells like boar excrement and is used for tracking by marking the target; Ibeho scent.
A short exchange follows leading Faputa to notice of two pressences stacked on top of each other approaching. Shortly after, Nishagora and Tepasté emerge from a section. In a brief moment of all characters taking note of each other, Nishagora notices Riko's whistle and gets enraged by assuming Riko's group must be underlings of the "Shrine Maiden."
Tepasté tries to disarm the situation by noting she has no idea who these children are but by Riko stating she is Lyza's daughter Nishagora becomes angry again as she knows Lyza's daughter was stillborn. Only with further explanation, and mention of the Curse-Warding Box she calms down, begins to note names of people she is reminded of by Riko's ciricumstances, before seemingly becoming lost in thought.
After becoming active again, she decides to take Riko's group to her boss if they want to follow her and Tepasté. Upon the reveal her boss is a White Whistle Delver, Riko immidiately wants to tag along and the rest of the group follows. Before they start following Nishagora, Nanachi thinks of what possibly led to the reaction Nishagora had after seeing Riko's white whistle. After some thinking, involving how all revealed White Whistles apart from Riko are relatively known in shape to an extent, only Riko's whistle has an origin of taking its form that Nanachi assumes only Riko's group, and possibly Bondrewd by peering into Nanachi's vision, knows about.
As such, she theorizes they are possibly looking for a white whistle of a never seen before shape with even its name being unknown. As the group travels, Riko and Co. theorize about the Shrine Maiden as it is something mentioned in Orth's fairy tales and in Hariyomari's song. During their further travel, Nishagora also asks them if they believe in souls to which Nanachi states she wants to believe in the existence of souls. Faputa however flat out confirms the existence of souls and states even layered creatures like Nishagora and Tepasté have them.
Soon after, the group arrives at the outpost of Hail Hex in the 6th layer. As they enter it, they are greeted by a member of Hail Hex who welcomes them. Inside the outpost, Nanachi marvels at the amount of equipment and shortly afterwards they are addressed by the boss of Hail Hex who is cooking food in a big pot. As the conversation progresses this boss tells them that the goal of Hail Hex is to reach the deepest depths of the Abyss and asks what Riko's goal is.
As Riko counts in her mind the many goals she and her group still has she says there's quite a lot. After hearing that, the boss of Hail Hex introduces the Curse Fleet Delver Troupe, Hail Hex, and afterwards herself as Captain of it, Srajo. She praises Riko and shows recognition as White Whistle. However, she also notes that they will have to but Riko through her paces first.
The Incinerator (火葬砲: Cremation Cannon) is a powerful incendiary cannon built into Reg's hands and feet, emitting a beam of light, indicating the area to eliminate, penetrating through objects. At its edges, an invisible force creates a centrifugal motion that, through the friction with the exterior, produces a secondary burn-off effect and extreme thermal energy, which have secondary destructive power. Objects within the range of the light break apart and are absorbed into the spinning axis. This leads to anything in its path to seemingly disappear, "as if it comes undone...Shortly afterwards, the surrounding air ignites to nothing." due to the device emitting a blast of heat at the end. The incinerator is also capable of "tensing up" the force field of the Abyss in an undefined manner. The size of the beam changes depending on Reg's will.
It is important to note that the Incinerator does not just burn objects; it is connected to the Abyss in an unknown way. The name implies that everything hit by the light returns to the Abyss. For instance, when Reg kills Mitty, he makes a comment about Mitty's soul "cycling again." Nanachi also comments that Reg's Incinerator "has the power to rewrite the rules of the Abyss". This weapon seems to work similarly to Sparagmos, the Origin-Guiding Light.
The Incinerator is a Relic that is part of Reg. According to Nanachi's theory, Relics in the Abyss can contain a pattern that signify the number of uses left before becoming useless. Along with passing out for 2 hours after 10 minutes after using the Incinerator, the pattern in Reg's helmet decreases. Electricity seems to recharge it, as the symbol grew again after Reg was exposed to electricity at Ido Front.
Reg's arms can extend up to 40 meters each. He can shoot them to the top of cliffs or grab things very far away. The cord attaching them is very durable and appears to be made of countless metallic threads. Using these arms does not reduce the pattern on Reg's helmet because they require a minimal amount of energy.
As commented on by several characters, Reg's body is extremely durable, even to the point that Ozen the Unmovable couldn't break him even when slamming him into the floor with all her strength. Despite his high durability, Reg is agile and weighs little. His wounds heal at a faster rate than a human's, and he has a very high pain tolerance. His navel is the thinnest part of his skin, making it a weak spot.
- (To Nanachi's cooking) "Irredeemable."
- (To Ozen) "Any way you look at it...You're really immature, Ozen!"
- Reg is able to fire his Incinerator multiple times in the duration before he passes out, and also can set it to not affect living beings.
- Reg is often associated with dogs. He is named after a dog Riko had when she was younger, and is also sometimes compared to a dog, even by those who aren't aware of the origin of his name.
- He is slightly disappointed that his muscles don't seem to grow.
- Reg being attached to Nanachi's fluffiness is akin to infantile traits
- Akihito stated in an interview that Reg was inspired by a Cave Story character named Quote.
- His favorite food is Mustard Manjuu.
- Reg's design stems from "the friendly lines and rusticness of the main character's robot from the series Tetsujin 28-go, as well as [Astro Boy's] unguarded sexiness".
- Even after his right arm was severed, he is still able to control it remotely.
- Reg's height is 1,37 meters.
- Reg's cape smells like hay.
- According to Shiggy, Reg could classify as an Aubade as his body, by his estimation, seems to be a bundle of Special Grade Artifacts and might even be one of the most valuable finds in the history of the Abyss.
|Riko's Party||Riko • Reg • Nanachi • Prushka • Meinya|
|Belchero Orphanage||Belchero • Jiruo • Nat • Shiggy • Kiyui|
|Orth||Hablog • Laffi • Torka • Menae & Sherumi • Mio|
|Seeker Camp||Ozen • Marulk • Simred • Zapo • Yelme|
|Ido Front||Bondrewd • Gueira|
|Ilblu||Wazukyan • Belaf • Juroimoh • Vueko • Moogie • Majikaja • Maaa • Mitty • Poriyon • Mepopohon • Embellith • Shurekaka|
|6th Layer||Irumyuui • Ajapoka• Faputa • Gaburoon • Tepasté • Cravali • Srajo • Nishagora • Unknown Member of Hail Hex|
|The Abyss||Lyza • Srajo • Wakuna • Human-looking silhouette|
|Unnamed Characters||Minor Characters|