Nanachi is a Narehate, a survivor of ascension from the sixth level of the Abyss. Due to certain circumstances, Nanachi was able to keep their personality and mental faculties intact. Their body, however, was deformed beyond recognition from their original body.
Nanachi looks very young but their vast knowledge of the physics and ecology of the Abyss seems to suggest they have lived there for quite a while. They also appear to be an amateur medic with significant surgical skills and an extensive knowledge of medicinal plants and animals. Despite this knowledge of the world of the Abyss, their cooking is pretty awful.
Nanachi's appearance is very rabbit-like, save for a long sturdy tail. Medium tan fur covers their entire body, with light tan being on two spots on their cheeks, the insides of the ears, and on the belly. They have straight white hair in a short bobbed style, with the sides of the bangs being much longer. Their eyes are yellow with the pupils being horizontal ovals, similar to a goat's. Their fingers are rather stubby.
Most of the time Nanachi is cool and reserved, keeping their distance emotionally and physically.Their attitude often borders on being sarcastic and even cynical, however behind this mask Nanachi hides a kind and gentle soul capable of deep compassion and selfless devotion.
Not much is known about Nanachi's past—they were born in the Far North region of Sereni, lost their family and home at a young age, and was taken to the Abyss by treachery, along with many other children.
Bondrewd was working on experimenting with ways to negate the curse of the abyss, and using children as his test subjects. While in the Abyss, Nanachi met Mitty, another child taken by Bondrewd, and the two became close friends. Nanachi and Mitty were best friends, until Mitty was chosen to be experimented on. Nanachi, worried for Mitty, followed and Bondrewd decided to use the two as test subjects because of their strong relationship. Each were placed in separate connected capsules, lowered to the 6th layer, and then quickly brought back up. The capsules were designed to transfer the curse onto only one subject, while the other received what Bondrewd called the blessing instead. Both survived and became Narehate but Nanachi retained their humanity because of Mitty's love for Nanachi ("Please... let my soul return to Nanachi").
Nanachi, in their new Narehate form, continued to work for Bondrewd at Idofront until they escaped with Mitty on their back, unable to bear the horrible experimentation Mitty was subjected to any longer. Nanachi lived with Mitty in the fourth layer for some time. They experimented on dying Delvers to figure out a way to kill Mitty. The bodies of these Delvers are buried in a graveyard behind their hut. Nanachi is careful to reveal themself because Delvers murders Narehate they come across.
But, Nanachi does reveal itself to Riko and Reg after they see Reg crying over Riko's body. Because their relationship closely resemebled Nanachi's relationship with Mitty, they aid them and eventually follow them to bottom of the Abyss after Mitty is released.
On top of top-notch tracking and stalking skills, since becoming a Narehate, Nanachi has been able to see the flow of the curse throughout the abyss, thus being able to avoid it. Nanachi is very knowledgeable about the different plants and animals, and which can be used as medicine or food.
- Nanachi is generally presumed to be female, but their gender and sex are never explicitly stated, and when talking about themself Nanachi uses the gender-neutral pronoun "oira." Tsukushi confirmed this by tweeting out "The sex of Nanachi is unknown. Let's imagine :)." Series translator Jake Jung has elected to use neutral pronouns for Nanachi.
- Nanachi has an "irresistible fragrance". In particular, the base of their tail smells really good.