Nat

Nat is an orphan from the Belchero Orphanage in the town at the edge of The Abyss, Orth. Like all the children of the orphanage, he's studied to become a delver since a young age and attained the rank of Red Whistle after his first descent. He wants to become a Moon Whistle like Leader, Jiruo, someday and build an orphanage somewhere in Orth.

Appearance
He has short brown hair with bright blue eyes and wears, like his peers, a red whistle around his neck. He is often seen in his plain white sailor collar shirt, green pants, and track shoes.

Personality
He really cares about the people around him, especially Riko. He was against Riko descending into The Abyss with Reg; he spoke of the difficulties of dealing with the Abyss alone and that he wouldn't be able to see Riko anymore. Although he was helping Riko and Reg descend into the Abyss, before the departure, he was hesitating and didn't say anything because he missed Riko so much.

History
He used to live in the Wharf, where he lived in the slums. He didn't have any family besides his older sister. When his sister died, he was alone in the streets, but the orphanage took him in, he becoming a delver.

Orth Arc
Nat is present right at the beginning of the story. He later travels with Riko into the 1st layer, because theier appointed delving areas being close to each other Due to unknown occuriensies, Nat gets hurt and passes out. He is found by a Crimson Splitjaw and only because Riko arrives at the scene, and draws attention to herself, not eaten by it. After he regains consciousness, and the Splitjaw having been fend off by Reg, he helps Riko carry the unconscious Reg to the orphanage. Nat and the others inspect Reg and try to wake him up with an electrical shock, which causes a blackout. Leader catches him and the others, uppon inspecting the blackout's source, and he is punished. Later on, they discuss what kind of being Reg could be and after discussing Shiggy concludes he must be made up of the most valuable findings in the Abyss's history, and is possibly an Aubade, a treasure of the netherworld. Because they would't be able to keep Reg's existence a secret, Shiggy comes up with a plan for Reg to pose as a homeless orphan who wants to become a delver and approach Leader; which is actually Nat's backstory. Luckily, it works out and Reg is officially taken in by the orphanage.

During Orth's Resurrection Festival, Nat and Shiggy explain things about it to Reg.

Later, the same night, Riko tells her friends that she will delve into The Abyss to find Lyza. Nat is firmly against Riko's plan to leave and they end u having an argument.

During Reg's first descent, he and Nat come across a Praying Skeleton. Reg, unprepared for the sight, freaks out, but Nat, amused by Reg's reaction, tells Reg about the Birthday Death Disease, hoping to scare him further. Instead, this only increases Reg's resolve to enter The Abyss and find the answers to several mysteries. Nat becomes very angry, and insists that Reg and Riko are crazy for wanting to do something so dangerous. After Reg's first descent ends, he is distracted because his memory didn't return as he'd hoped. He completely misses that Nat is lagging behind, suffering from 1st layer ascension strains, until Nat vomits.

That night, Riko tells her friends that she will leave the following day, just before dawn. When Shiggy asks how she will enter The Abyss, Reg volunteers to lower her with his extending arms, and announces he will go with her, both to find his own answers and to protect her. Nat tries again to talk Riko out of going, but she stubbornly refuses, until Nat finally blurts out that no one could survive for a decade in The Abyss, and that Lyza must be long dead. Kiyui bursts into tears while Reg tries to comfort him, Riko runs out of the room, and Nat is left feeling guilty.

As Riko and Reg prepare to leave the orphanage, Reg suggests that Riko make up with Nat. She refuses, until Reg points out that they will never see Nat again. Riko agrees to forgive Nat if he apologizes. Later, Reg goes to Nat's room but the bed is empty.

Riko and Reg meet up with Shiggy, who volunteered to accompany the pair as far as the edge of The Abyss in the South District. Shiggy advises them to enter The Abyss through the entry point at the wharf slums, which are not monitored as closely. He has already gotten someone familiar with the area to lead them, which turns out to be Nat. Nat apologizes to Riko, who instantly forgives him. She believes he has finally come around, but Nat makes it clear: he is willing to help her, but is still against her leaving. Reg says they will send Nat letters, but Nat disagrees, pointing out that the likelihood of mail reaching the surface from the depths is very low. Riko promises to write many letters, so that at least some will reach them. Nat explains that the wharf was built by illegal delvers, and that he and his late sister used to live there. He dreams of becoming a Moon Whistle, and returning to build an orphanage there. Riko encourages his dream. The group soon reaches the edge of The Abyss. As the group says their goodbyes, Nat struggles to tell Riko how he really feels, but can't. They are both in tears, and Riko says they will be forever connected by The Abyss. Realizing that they have disturbed the residents and are drawing attention, Reg and Riko quickly descend into The Abyss while Shiggy and Nat watch.

Since then, while Nat has not interacted directly with Riko or Reg, he has been shown on the surface hearing stories from Hablog about The Abyss and it's inhabitants, foreshadowing the dangers that Reg and Riko would face; aswell as talking with Laffi about Kiyui.

Trivia

 * When Reg got registered at the orphanage, the story he used was based on Nat's backstory.
 * Natto is a popular Japanese snack of fermented soybeans.
 * Nat had a crush on Riko.