Inheriting substantial debts from her deceased father, Kasumi Miyamori bears a heavy financial burden that leaves her and her sister Kaho exposed to aggressive debt collection. This compels her into a transactional agreement with Hiroyuki Okura, a student who offers financial assistance in exchange for sexual servitude from both sisters until their obligations are fulfilled.

Kasumi possesses brown eyes, pale skin, a slim build, and brown hair cut in a bob. She primarily wears a high school uniform featuring a blazer, necktie, and thigh-high stockings. Later official media showcases her in diverse attire, including a Chinese dress, wedding gown, and apron, signaling shifts in her circumstances.

Across subsequent visual novel installments, her responsibilities evolve: she transitions into a teaching position and later adopts a homemaker role centered on cooking, reflecting progression past her initial debt struggles. Medical elements like catheter usage emerge in these narratives, though specific health contexts remain unelaborated.