Yōko Otosumi is the maid serving at the mansion inherited by Shougo Yoshisuzu after his grandfather's passing. With brown hair and brown eyes, she lives in the mansion and tends to Shougo's daily needs, such as waking him each morning and guiding him to the cafeteria. She maintains a consistent sexual relationship with him, during which Shougo enters a semi-conscious state after orgasm and experiences visions of a mysterious beautiful girl. This girl is later revealed to be Reiko, whose portrait hangs in the mansion. Yōko's involvement extends beyond domestic tasks into a complex relational dynamic with Shougo.

A supernatural undercurrent links Yōko to the mysterious phenomena surrounding Reiko, whose spirit exhibits possessive behavior, notably affecting other women like Momoka. While Yōko’s precise role in these events remains ambiguous, the situation fuels interpersonal tension—particularly with Ayano, Shougo’s fiancée, who grows jealous upon observing his interactions with other women.