Toru Shirai, known as Shiro, is a 43-year-old man residing beneath the Arakawa Bridge, compelled by an unwavering obsession to walk solely on white lines. He fears deviating from this ritual will transform his wife into a white Cornish hen, a belief that drove him six years prior to abandon his corporate salaryman life and adopt bridge-dwelling. To sustain his practice, he transports a line-painting machine, crafting temporary paths wherever he goes. Though estranged from his family, they persist in quiet support: his wife sends entry forms for white-line-stepping contests, while his daughter maintains steady communication.

Polite and introverted by demeanor, Shiro conceals a ruthless competitive drive, rigorously training year-round for the village’s annual race. Rivals often withdraw upon witnessing his unyielding focus, acknowledging his unmatched resolve. His dynamic with Shimazaki, an Ichinomiya Company employee, involves her unreciprocated romantic interest, which he overlooks entirely.

Within the bridge community, Shiro emerges as both an enigmatic anchor and occasional problem-solver, his peculiar compulsions juxtaposed with flashes of practical skill. While spin-offs and films refrain from expanding his past, his rigid routines and enduring, if distant, familial bonds remain unaltered across narratives—a blend of absurdist humor and quiet emotional undercurrents.