Tsukasa Watanabe, Tsuyoshi Igawa’s loyal best friend, navigates life alongside his younger sister Yumi while nursing an unreciprocated crush on Tsuyoshi’s sister, Keiko. His fixation compels him to barter with Tsuyoshi, offering cash in clandestine exchanges for Keiko’s underwear—a quirk paralleled by his hobbies: amassing adult magazines and decorating his room with martial arts film posters.

After stumbling upon a time machine with Tsuyoshi, the duo hurtles twelve years into the past, confronting their younger selves and a preteen Keiko. When the child version of Keiko steals a crucial part of the device, Tsukasa’s rash instincts flare. He scrambles alongside Tsuyoshi to recover the component, dodging temporal chaos. His impulsivity resurfaces in frantic sprints from his sister’s friends and hasty retreats into odd hiding spots.

Throughout narratives, Tsukasa operates as a comic foil, his relentless pursuit of Keiko and penchant for dragging Tsuyoshi into ill-conceived plans cementing his role. His character remains static, defined by these traits without deeper evolution or backstory.