Chakuro is the central character of the narrative and serves as the archivist for the Mud Whale, a drifting island community adrift on a vast sea of sand. As the primary recorder of his people's history, his role is both a formal duty and a personal compulsion. He physically appears as a young boy with short, messy brown hair and green eyes, often seen wearing a pair of goggles atop his head.

The most defining aspect of Chakuro's identity is his condition of hypergraphia, an overwhelming and irresistible urge to write. This drive is so powerful that both he and his grandfather view it as a kind of illness. His compulsive note-taking serves a vital function for the Mud Whale, as his objective and detailed records are regularly consulted by the community's council of elders. In stark contrast to the neutrality of his written work, Chakuro is a deeply expressive and emotional person. He is intensely curious about the world around him, frequently contemplating philosophical questions about existence, such as why the Mud Whale floats or the true importance of feelings. His sensitivity often gets the better of him, and he is known to cry openly at funerals, even when such displays are discouraged by social norms.

Chakuro's motivations are heavily rooted in his desire to understand his own world and the unknown world beyond it. His curiosity is the engine of the plot, as his inquisitive nature leads him to explore a mysterious derelict ship, where he encounters Lykos, the first person he has ever met from outside the Mud Whale. This meeting shatters his understanding of reality and compels him to seek the truth about the vast society that exists beyond his island home. As the story progresses, he is driven by a need to protect his friends and community while grappling with the difficult ethical and moral questions that arise from conflict. A recurring conflict for him is the tension between his upbringing in a pacifistic community and the realization that violence may sometimes be necessary for survival.

Chakuro holds significant power derived from thymia, the emotional energy that grants abilities to the marked residents of the Mud Whale. However, his control over this power is notoriously poor, earning him the ominous nickname of the Destroyer. His lack of control is a direct consequence of his intense emotions, which can manifest destructively when he is under extreme stress. In his early years, he was taught to use his thymia by Benihi, one of the elders on the island. His hypergraphia is also intrinsically linked to his abilities, and during periods of intense emotional turmoil, he can experience severe hypergraphia episodes where his compulsion to write becomes overwhelming.

His key relationships are central to his development. His friendship with Sami dates back to childhood, and her romantic feelings for him create a deep bond that is tragically cut short by her death. This loss is a pivotal and traumatic event that forces him to confront his own limitations and the harsh realities of his world. He is also close friends with Ro and Nezu, the latter of whom enjoys creating small inventions. Another significant connection is with Suou, who becomes the new leader of the Mud Whale and whose sister, Sami, was Chakuro's close friend.

His most transformative relationship is with Lykos. As the first outsider he ever meets, she represents everything unknown and dangerous about the world. Despite initially being an enemy, she becomes a close friend and a source of romantic tension, as his growing feelings for her further complicate his sense of duty and his desire to protect his people. Throughout the series, Chakuro evolves from a passive observer and recorder of events into an active protagonist who fights for the future of the Mud Whale. He learns that his official archives have limits, and he begins to rely more on his personal diary to capture the truths he discovers. His journey forces him to confront his own naivety and accept that tragedy and joy are inseparable parts of the human experience. Ultimately, his development affirms his belief that the full range of human emotion, including pain and hardship, is worth preserving. In the end, he chooses to live a life of wandering, traveling the world to continue documenting its history and adding to the archives, never marrying but dedicating himself to understanding and recording the world he once only dreamed of seeing.