I'm gonna go ahead and say Netorase.
Seems incredible to me with how hentai allows for a lot of unusual practices that open relationship stuff such as this is so niche. And I'm not saying MC having sex with several girls and all of them being ok with that, since that's common. But actual couple sharing or swapping.
Bitting is best cause its not only a way of marking possession but to feel and taste of skin on your teeth is another experience itself. Who doesn't want to leave a mark behind proof that they were here? And maybe remind the person who they are ~ 😇