Youko Otosumi is the primary maid residing in the mansion inherited by Yoshisuzu Shougo after his grandfather's demise. She manages all household affairs and provides Shougo's daily care. Youko has brown hair, brown eyes, and wears glasses.

Her duties extend beyond standard household management to include a consistent sexual relationship with Shougo. These nightly encounters trigger Shougo's subsequent visions of an unidentified girl, later linked to a portrait of Reiko within the mansion. Youko attributes her commitment to Shougo's care, including this intimacy, to a promise made to his grandfather. She addresses Shougo as "Master," reinforcing her subservient role.

While central to the household, Youko coexists with other women involved with Shougo, such as his fiancée Ayane and a schoolteacher. Her actions remain focused on fulfilling her perceived obligations from the promise to Shougo's grandfather. The supernatural events tied to Reiko's ghost, while connected to Shougo's post-intimacy visions, involve Youko only indirectly. Her character trajectory remains static throughout the narrative.