Eiji Kakihana is a 41-year-old janitor and an old friend of Hiroshi Odokawa and Ayumu Goriki. Despite personal struggles, he maintains a generally good-natured and optimistic personality. Spurred by loneliness and societal pressures concerning his age, appearance, and modest cleaner's income, Kakihana actively uses a dating app seeking marriage. Low self-esteem drives him to falsify his profile, claiming a 20 million yen annual income and a university degree to enhance his appeal; his actual earnings fall below three million yen, and he possesses only a high school education.

In his school years, Kakihana enjoyed popularity and played baseball, but his adulthood is shadowed by feelings of inadequacy. This vulnerability leaves him susceptible to a badger game scam executed by Shiho Ichimura and the yakuza member Haruhito Yano. After meeting Ichimura via the app, he borrows money from loan sharks to uphold the facade of wealth presented in his profile. Failing to repay these debts results in his kidnapping and physical assault by Yano's group. Following his rescue—facilitated by Odokawa and the yakuza member Dobu—Kakihana reflects on his choices amidst the city-wide chaos triggered by Odokawa’s car chase. In the aftermath, he commits to repaying his debts through multiple jobs, adhering to Odokawa’s advice to resolve his financial obligations independently.

He appears as an anthropomorphic white gibbon due to Odokawa’s visual agnosia, a psychological condition causing Odokawa to perceive humans as animals. The finale reveals Kakihana’s human form after Odokawa’s recovery from this condition.