Nanachi is a Hollow, also known as a Narehate, a being who survived the curse of the sixth layer of the Abyss and was physically deformed as a result. Unlike most others who undergo such an ascent, Nanachi retained their mental faculties and personality intact. Originally a child from the far northern region of Sereny who lost their family and home at a young age, they were taken into the Abyss by the White Whistle delver Bondrewd along with many other children. Under Bondrewd’s experiments, Nanachi and a companion named Mitty were subjected to the sixth layer’s curse; Nanachi emerged with a transformed body—rabbit-like ears, fur, and an overall beast‑person appearance—but with a sound mind, while Mitty lost all identity and became an immortal, mindless being.

Nanachi’s personality is cool and reserved, often maintaining emotional and physical distance from others. They possess an ironic, sometimes sarcastic or cynical sense of humor. This detached exterior hides a deeply kind and gentle soul capable of profound compassion and selfless devotion. Their motivations are shaped by lingering guilt and responsibility for Mitty’s fate, as well as a desire to atone and to help those who venture into the Abyss. They are driven to assist the young delvers Riko and Reg, deciding to accompany them on their journey after forming a bond with the pair.

In the story, Nanachi first appears as a mysterious, isolated figure living in the Abyss. Their role evolves from a solitary survivor into a crucial ally, guide, and healer for Riko and Reg. Their vast knowledge of the Abyss’s physics, ecology, flora, fauna, and medicinal plants makes them an indispensable source of survival expertise. Nanachi is also an accomplished healer with exceptional surgical skills and pharmacological knowledge. They possess a unique ability to communicate with and understand the creatures of the Abyss, and their survival techniques are vital for enduring the harsh conditions of the depths. Their physical form, however, limits them in direct combat, so they rely on tactical support and healing.

Key relationships include the tragic bond with Mitty, who becomes a symbol of loss, guilt, and compassion for Nanachi. This connection serves as an emotional anchor in their narrative. With Riko and Reg, Nanachi experiences camaraderie and begins to open up emotionally, forming a deep, supportive friendship. The trio functions as a cohesive unit, with Nanachi’s experience and emotional intelligence balancing the group.

Nanachi undergoes significant development, evolving from a lonely, guilt‑ridden figure to one who values companionship and finds a new purpose in helping Riko and Reg. They confront painful memories of their past, particularly regarding Mitty and the choices that led to their current state. Their journey through the Abyss reflects themes of companionship, loss, identity, and resilience. Notable abilities include enhanced senses, accelerated development, extrasensory perception, and a form of precognition, as well as a deep understanding of the Abyss’s curse and how to navigate its dangers.