Although this isn't on the list from one of the posters, it's definitely part of the Mother and Child Orgy Club series (AKA Someone Else's Mom series). I'm translating Mama Anal now and page 2 specifically says this is Rioko, the main Mom character. Anyone know where it fits in continuity? If no one knows I'll just guess. It would probably work as Ch1a (since she's trying to seduce Tomokazu at the end). But Ch7 might be possible as well since they are definitely having sex there (I'll no more once I translate it).