Ichi Seya is a Japanese human male characterized by brown hair and violet eyes. He lives as a tragic swordsman, profoundly burdened by guilt stemming from past actions that resulted in the death of his childhood friend, Tsukishima. This event triggers significant emotional isolation. Seya, Tsukishima, and Kuroda were once a close-knit trio in their youth; the loss devastates both surviving friends. While the precise nature of Seya's involvement in Tsukishima's death remains tied to his own deep sense of responsibility and remorse, its impact is undeniable. His path toward emotional healing begins through his relationship with Yuzu, a Hybrid Child he owns. This android entity grows and develops emotionally based on the love and care received from its owner. Seya's interactions with Yuzu facilitate his gradual relearning of love and his confrontation with unresolved guilt. Repentance forms a central theme in his narrative, encapsulated in his declaration: "I have to repent these sins of mine." Seya's background connects to historical or clan-based conflicts, as Tsukishima later became a minister of the Rebel Clan. Seya's adult life centers on swordsmanship, aligning with his depiction as a swordsman shaped by tragedy. The evolving bond with Yuzu becomes instrumental in his healing, symbolizing an escape from self-imposed emotional isolation. His story is one narrative among several exploring love, loss, and artificial life within the broader work. Across official media, including the manga and its OVA adaptation, Seya features prominently in the second chapter/episode. His character development focuses on overcoming past trauma through caring for Yuzu, illustrating the series' exploration of how artificial beings reflect and amplify human emotions. He remains alive at the conclusion of his storyline and maintains a continued friendship with Kuroda despite their shared loss.