Inmo, known in the original Japanese as Fushi, is the central protagonist created by the mysterious figure known as the Beholder or the Man in Black. This immortal being was placed on Earth with the fundamental task of preserving the world and gaining experiences. Inmo begins existence as a small, egg-shaped object, a formless entity that learns and evolves by absorbing the forms of things that die in its presence. The name Inmo is given to the being by a young girl named March, who finds him on her way to becoming a virgin sacrifice.

In terms of background, Inmo is not born but created. Its original nature is that of a blank slate, a divine proxy sent to understand and interact with the world. As an immortal, Inmo is immune to death by age or disease, possessing a resurrective immortality that allows it to heal from fatal wounds, often faster after repeated exposure to the same type of injury. The character's journey is one of discovery, learning even the most basic aspects of living, such as language, social customs, and human emotion, from scratch.

Personality-wise, Inmo initially appears emotionless and detached, mirroring its lack of life experience. However, as it interacts with various people, Inmo gradually develops a complex emotional range. It learns love, friendship, grief, and rage through its connections with others. Inmo is deeply affected by the suffering and death of those it cares about, leading to a profound sense of loneliness and responsibility despite its own immortality. The experience of watching loved ones grow old and die, particularly the slow decline of Pyoran into dementia, is a source of immense sorrow for Inmo. Furthermore, Inmo is not immune to physical discomfort; using certain forms, such as that of a boy who died with dozens of arrows embedded in his skin, causes Inmo constant pain.

The core motivation for Inmo evolves over time. Initially, its drive is purely survival and the fulfillment of its mission to grow and learn. As its emotional bonds deepen, its primary motivation becomes the protection of its friends and the desire to stop the Nokkers, also known as the Knockers, who are the primary antagonists. These beings are a constant threat, seeking to destroy or corrupt Inmo and humanity. Later in the story, Inmo's motivations expand to include a desire to defeat the Nokkers permanently, leading it on a quest for an omnipotent sphere left by its creator, a power that could potentially fulfill any wish. Inmo also learns it can create duplicates of parts of its form to use as weapons, a skill refined with the help of its friend Gugu.

Inmo's role in the story is that of an observer who becomes a participant. It is the lens through which the narrative explores themes of life, death, and what it means to be human. As an immortal being, Inmo serves as a living archive of the people it has met, carrying their forms and, in a way, their legacies forward. As the story progresses, Inmo's power grows to the point where it can create and sustain the bodies of its deceased friends, effectively making them immortal soldiers in the fight against the Nokkers, though the morality and emotional weight of this ability are complex.

Key relationships define Inmo's development. March is the first human to show it kindness and gives it its name, acting as a foundational figure. Pyoran, an elderly woman who teaches Inmo to read and write, becomes the closest thing it has to a mother figure, and her eventual death from old age and senility is a traumatic lesson in the nature of human mortality. Gugu, a young man with a disfigured face who wears a mask, becomes a brother figure, teaching Inmo how to use its shapeshifting abilities in combat and sharing in its adventures. Hayase, a government official from Yanome, represents a dark mirror to these bonds, developing an obsessive and violent love for Inmo that leads her to kill anyone close to it, a twisted devotion that gets passed down to her descendants for generations. These numerous descendants, such as Hisame and Kahaku, continue to play significant roles in Inmo's long life, pursuing the immortal across centuries.

Inmo's development is the central arc of the narrative. It begins as an unknowing rock, becomes a wolf, then a boy, and slowly learns to be human. This growth is not linear; it is marked by frequent setbacks and deep psychological wounds caused by losing one friend after another to violence or old age. Over centuries, Inmo becomes a weary but determined figure, having witnessed the rise and fall of civilizations and the repeated deaths of those it loves. The character is forced to constantly find new purpose in an endless existence, such as seeking the omnipotent sphere or confronting the origin of the Nokkers.

Notable abilities include voluntary shapeshifting into any form it has acquired from a being that has died near it. These forms can be anything from a stone, to a bear or bird, to the specific bodies of deceased humans like March, Gugu, or Parona. When Inmo transforms, it also replicates the clothing and any objects the person was holding at the time of death, but these can be removed. The true form of Inmo is the small, original orb, from which all other forms are derived. Inmo's combat style evolves from simple physical attacks using animal forms to more complex strategies, including the spontaneous creation of weapon duplicates and the resurrection of allies bodies to fight alongside it.