Tsukasa Watanabe stands as Tsuyoshi Igawa's closest friend. His younger sister Yumi Watanabe possesses a maturity exceeding his own, harboring romantic feelings for Tsuyoshi and dreaming of marrying him. Tsukasa himself is intensely infatuated with Tsuyoshi's older sister, Keiko Igawa, who persistently ignores his advances. This obsession drives Tsukasa to inappropriate actions, including offering payment to Tsuyoshi for access to Keiko's undergarments; he also collects pornographic magazines. Beyond these pursuits, Tsukasa is an enthusiast of martial arts films, a passion reflected in the posters of famous performers decorating his room. He and Tsuyoshi once accidentally activated a mysterious machine discovered in a warehouse, an event that propelled them twelve years into the past. During this unexpected journey, they encountered their younger selves and uncovered details concerning Keiko's first romantic interest.