The episode starts off with flashbacks of Reg's and Riko's adventures up to the ending of episode 12. We then see Nanachi dragging Reg back to her hut, because Reg had fired his Incinerator to fend off the Orb Piercer. While doing so, Nanachi rembers their past and the events that lead them to live with Mitty on the 4th layer.
A still human Nanachi is shown lying down reading a book, in what appears to be slums of a country. Suddenly, Children in the hallway, outside the shared room in which Nanachi lives, leave to go outside in a hurry and Nanachi follows. As they gather outside, a boy standing next to Nanachi comments on how bad they smell so Nanachi moves further back and looks upon the reason why so many have gathered; a White Whistle Delver.
The White Whistle Delver introduces himself as Bondrewd, stands in front of the children, and tells them: "I've come here in search of children suitable for forging a path to the netherworld's next era". He invites the children brave enough to face the Abyss to accompany him.
Next we see Nanachi looking into the Abyss from a building in Orth, showing they chose to follow Bondrewd. While gazing towards the hole, Nanachi overhears an argument between other kids denying, the still human, Mitty the chance to work with them.
The scene transcends to showing the children being gathered in front of a vessel to begin their descent into the Abyss. Bondrewd explains to them they will be guided by his personal Delvers and their descent is approximately 13 kilometers, in order to reach his base on the 5th layer.
During their descent, Mitty and Nanachi have their first interaction with Mitty asking about Nanachi's ambitions, and then immediately explaining her own; to be a White Whistle Delver. Nanachi, annoyed by her joyfulness, explains they don't care what they do because everything will be better than the prior life they lead. Due to Mitty seemingly taking a liking to Nanachi's openness, she explains of the treasures to find in the Abyss and offers to be partners with Nanachi; to which Nanachi agrees.
Some time passes, and the two are shown reading a book called "Capital of the Unreturned", which is written in Nether Glyphs. Nanachi can read them and Mitty notes how amazing that is as even only a small group among the highest ranking Delvers can.
After they arrive at their destination, a voice from an intercom tells them they will suffer the strains of ascension if they climb more than 10 meters. The children walk through a tunnel and gather at the end of it to find a beacon that looks similar to the one during the opening. As both Mitty and Nanachi look up to it, they hold hands in awe of this view. Then Bondrewd appears and shows the children to the room they will be living in.
While in this room, Mitty asks about the "Abyssal Faith" and Nanachi explains it is believed, when a life is lost in the Abyss, the soul is said to return to the bottom of the planet. Then, the soul changes form and departs on a journey to someone who has wished for life. The pit replaces God and its a comfort to the Delvers. Mitty praises Nanachi for their knowledge, making Nanachi a little bit embarrassed. Over time, Bondrewd calls a child out to follow him until only Nanachi and Mitty are left. One night, as Mitty and Nanachi are sleeping together, Bondrewd calls for Mitty and tells Nanachi, who wants to go with Mitty, to be patient for their turn.
Nanachi, wanting to look for Mitty, sneaks out of the room and explores the Ido Front. In their search, they overhear Bondrewd talking to another person. In this conversation, the other person questions Bondrewd's ethics to use the children in experiments, but is calmly rebuked by Bondrewd. Nanachi, shocked by what they overheard, starts running in a panic to find Mitty. When Nanachi finally finds Mitty, she is inside a clear cylindrical container. Bondrewd quickly notices Nanachi and expresses how pleased he is with their perfect timing, due to needing them as well for the experiment. Nanachi is placed inside another container next to Mitty and Bondrewd explains they are in elevators that can descend into the 6th layer. The destination is a controlled area, making it perfect for research on human subjects and their reaction to the 6th layer's Curse: "Death, or loss of one's humanity". When, with the two still being in shock what is going to be done to them, they are dropped into the depths to their destination. After arriving on the 6th layer, around them are Narehate who have lost their humanity and, as Nanachi becomes more and more frightend, Mitty calms them down by telling them everything will be fine. As they ascend, Nanachi turns into a blessed Narehate. On Mitty's side on the other hand, she starts bleeding severely and screams out in pain to the point of begging to be killed. Nanachi, shocked by this, can do nothing but watch in despair as their best friend turns into her cursed form.
After the elevator has arrived back up, Bondrewd opens it and expresses how pleased he is with the results of the experiment. In the next scene, Nanachi is drawing a crude picture of Mitty, but Bondrewd asks them to help with research instead. It is seen that Bondrewd is researching Mitty, and he tells Nanachi that Mitty lost her humanity but is also incapable of dying. Bondrewd informs them he has tried to kill Mitty nine times, but due to her regeneration she won't die. The only permanent damage he was able to cause Mitty was done with one of his Artifacts; Sparagmos.
After a long time at the Ido Front, Nanachi escapes with Mitty as they can no longer take the experiments they help in nor the abuse of Mitty. In the next scene, Nanachi is seen establishing their hideout. Over the following years, Nanachi tries to kill Mitty many times to end her suffering existence, but with no success. It is also seen how Nanachi starts their experiments to kill Mitty on Delvers they find and are beyond safing. Upon their deaths, Nanachi buries them behind their hideout.
Back in the present, after Reg wakes up, Nanachi explains he has the perfect weapon for killing Mitty; his Incinerator. Nanachi says that Mitty has lost her humanity and that her soul is imprisoned in her body, so Nanachi wishes to end her suffering. Reg, taken back by the request, asks Nanachi for some time to think about it, fearing Nanachi might take their life after Mitty is gone. Nanachi apologizes for asking Reg to do such a thing and they head back to the hideout.
Later, Nanachi says they will preapare a meal, but Reg insists he does it, out of fear it could turn out tasting bad again, but he fails as well at making anything good and it turns out even worse than Nanachi's creations.
Afterwards, Reg is seen cleaning Riko while Nanachi is reading to Mitty. As Mitty comes out of her place while Nanachi is asleep, Reg wonders if it is really okay to kill Mitty; still unable to make up his mind.
In the next scene, Reg stands next to Nanachi as they are fishing and asks them if Mitty is unhappy. Nanachi, predicting his next question is about the necessity to kill Mitty, explains Mitty can live forever but they can't and when they die, Mitty will be alone for eternity. They ask again for Reg to kill Mitty, so that she won't be left alone in an existence of suffering at some point. Reg makes up his mind, but requests Nanachi to promise not kill themself after Mitty is gone. Nanachi agrees, remarking sadly how cruel of a promise it is.
Nanachi is seen preparing a blanket with stuffed animals around it, and setting Mitty on it while talking to her, as Reg prepares his incinarator. As Reg's incinerator charges, suddenly Nanachi calls for him to stop, runs over to Mitty, and starts crying at the realisation they will never see Mitty again. After calming down, Nanachi walks back and tells Reg they are ready now and he can do it. Reg fires his incinarator and Mitty, engulfed in the light of the beam, is destroyed. After Mitty has been completely incinerated Nanachi bursts out in tears over the loss of their friend and Reg comforts them with a hug while tears run down his face as well.
After Reg passes out, he has a dream of Riko's mother, Lyza, telling Reg not to be sad as she offers him food. When Reg wakes up Riko is already awake again and is cooking with Nanachi. Nanachi asks Reg to stop Riko, who is very curious about Nanachi, from rubbing them, but instead Reg wants to join in. After the meal is prepared, they all dig in and Nanachi loves it, but pretends it is only okay to safe face. While they eat, Riko asks if someone else besides Nanachi lives in their hut. This shocks Reg and Nanachi into silence and Nanachi asks how she knows, but Riko wonders why as well and tells them about the dream she had while being unconscious.
She explains while she was suffering from the posion she almost forgot who she really was, to the point of forgetting her shape. During that time, she heard another girl crying. Riko couldn't see anything clearly, but just the presence of the other girl was comforting her. Shortly before she woke up she could see the other girl moving on; being Mitty when Reg destroyed her.
Later on, all three visit a hot spring and Reg helps undress Riko. Riko notices Reg's reaction, causing Reg to be heavily embarrassed. Nanachi refers to the time Reg blew air into Riko's lungs and spins it off as Reg kissing Riko, making Reg more embarrassed. While watching the two, Nanachi asks Mitty silently to wait for her a bit longer and makes up their mind to go with Reg and Riko.
Back at the hut, Nanachi and Reg remove the Parasitic Water Shrooms from Riko's arm. After the operation, Riko is trying to move her hand, but she is only able to twitch her thumb. Riko asks Nanachi to come with them on their adventures to which Nanachi agrees.
Before starting their journey, they release a Mail Balloon and its progress to Orth is shown.[Anime only]
They then go and prepare their things to leave and Nanachi looks back at her hut for the last time before they depart to new adventures.
After the credits, the final scene shows Bondrewd's surprise that Mitty's life signature has disappeared and he congratulates Nanachi.
- Volume 3, Chapter 23: A Dreadful Experiment
- Volume 3, Chapter 24: Liberation of the Soul
- Volume 4, Chapter 25: A Return from Darkness
- Volume 4, Chapter 26: A Fresh Start
- Nanachi and Mitty escaped from Ido Front, the Forward Operating Base due to Bondrewd's dreadful experimentation
|Season 1||1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13|
|OVA||1 • 2 • 3 • 4|
|Movies||1: Journey's Dawn • 2: Wandering Twilight • 3: Dawn of the Deep Soul|