Yotsuya, the tenant of room four at Ikkoku-kan, is better known simply as the mysterious man of the boarding house. Virtually nothing is known about his background: his age, occupation, and personal history remain a complete enigma to the other residents and the audience. He is almost always seen wearing a business suit or a formal yukata and speaks in an excessively polite and formal manner, even when carousing. His personality is defined by a blend of voyeurism, gluttony, and a love of mischief. He takes great pleasure in tormenting his next-door neighbor, Yusaku Godai, by breaking holes through the adjoining wall to spy on him and on the other tenants, stealing food from him, and blackmailing him with information obtained through eavesdropping. He also routinely joins forces with the other troublemaking tenants, Akemi Roppongi and Hanae Ichinose, to throw noisy parties in Yusaku's room. Yotsuya's motivations are never explicitly stated; he seems to act purely for his own amusement, with no apparent goals beyond causing chaos and satisfying his curiosity. In the story, he serves as a recurring source of comic conflict and an obstacle to Yusaku and Kyoko's relationship, as his pranks often lead to misunderstandings or property damage that fall on Kyoko to repair. His key relationships are primarily antagonistic: he torments Yusaku directly and inconveniences Kyoko indirectly, while maintaining a boozy camaraderie with Akemi and Mrs. Ichinose. Over the course of the series, Yotsuya undergoes no meaningful character development; he remains the same enigmatic, meddlesome figure from beginning to end. His notable abilities include an uncanny talent for creating and exploiting secret passageways through walls, a knack for appearing unexpectedly, and a well-practiced skill at mooching food and drinks from others.