Eiji Kakihana is a 41-year-old janitor born in 1980, maintaining lifelong friendships with high school companions Hiroshi Odokawa and Ayumu Gouriki. His good-natured optimism and energetic demeanor starkly contrast Odokawa's reserve, often veering into naive territory. Actively seeking marriage through a matching app, he pursues companionship with Shiho Ichimura, unaware she orchestrates honey traps for criminals. This entanglement draws yakuza members Dobu and Yano into his life, leading to blackmail, crippling debt, and eventual kidnapping by Yano's group. Odokawa and Dobu collaborate to secure his rescue, after which Eiji commits to independently repaying debts, marking a turn toward accountability despite prior financial imprudence.

His social awkwardness surfaces vividly in romantic pursuits, particularly with Shiho, while humorous exchanges with Odokawa and Gouriki highlight his talkative nature and occasional delusions about aspirations. Though visually perceived as a white gibbon due to Odokawa's visual agnosia—a psychological condition interpreting humans as animals—Eiji remains biologically human.