Saori Shirakawa relocates to the Onodera residence with her younger sister Yui following their father's remarriage, becoming Takumi's housemate. She vehemently rejects being addressed as his sister or integrated into the family unit, maintaining a consistently aloof and cold demeanor toward household members. Her driving ambition is achieving independence to depart with Yui, prompting her to take multiple part-time jobs after school.

Despite overt hostility—particularly toward the new paternal figure—Saori exhibits an inherently warm and friendly nature through loving interactions with Yui. She harbors deep-seated resentment bordering on hatred toward her new father, extending to initial reservations about Takumi. However, she gradually cultivates strong romantic feelings for him, creating significant internal conflict over her conduct in his presence.

Her character arc navigates tensions between her quest for familial independence and burgeoning emotional attachment to Takumi. Their relationship evolves from initial confusion and avoidance toward increasing closeness and intimacy during cohabitation, notably highlighted throughout the winter holiday period.

Physically, Saori possesses black hair, blue eyes, stands 1.60 meters tall, and has measurements of 90-56-87.