Acting as a substitute for my stepsister, Miho Tono (ALDN-576)

At the request of her sister and her husband, with whom she has no sexual relationship, the older sister finds herself inexplicably forced to serve her sister's husband… "Why did it turn out like this…?" the older sister wonders. Yet, she has reasons for accepting her sister's request. Confused by her sister's unreasonable request, the older sister gradually opens her heart and body to her brother-in-law, who needs her. She knows it's wrong, yet she can't resist the pleasure. Unbeknownst to her, the older sister has become addicted…