Shuhei manifests in two separate existences across time, linked by fire-activated temporal displacement. In the modern era, he is a six-year-old neighbor to Suzuko, marked by a recent appendectomy scar.

A gas explosion catapults him and Suzuko into Japan’s Sengoku period, though he arrives ten years earlier. Discovered as a child, he is adopted as Shukumaru—a brash but fiercely protective village scavenger who gathers battlefield supplies for his community. His personality, forged by hardship, combines impulsiveness and blunt speech with deep loyalty to villagers.

Physical ties bind his identities: the appendix scar persists on Shukumaru’s body, and he recognizes the bell of young Suzu (Suzuko’s past self). These become critical when Suzuko unravels their timeline connection.

His relationship with Suzuko shifts from modern-day proximity to a protective and romantic bond in the past, complicated by temporary mistaken kinship. Believed to be siblings due to Shukumaru’s adoption into Suzu’s family, the confusion breaks when Suzuko identifies his scar, confirming he is Shuhei’s adult self, not a blood relative.

Functionally, he triggers Suzuko’s understanding of time travel and propels the story’s resolution. After a brief return to the present for medical care, both deliberately engineer another explosion to permanently return to the Sengoku era, where they cement their relationship.