NHDTC-233 — The younger sister, aroused by hearing her older sister's moans that could be heard even through the partition curtain, was repeatedly ejaculated into.

Two close sisters share a room, separated by a curtain. Whenever the older sister's boyfriend comes to stay, the younger sister is always right next door, so they have to hold back their moans while having sex. The younger sister masturbates, using her older sister's erotic sighs escaping from behind the curtain as her arousal. When the boyfriend notices, he ejaculates inside the younger sister while she's asleep, bringing her to orgasm multiple times. Eventually, the younger sister herself begins to ask for unprotected sex and internal ejaculation.