The H-Manga i'm trying to find has a girl moving/visiting a house, and in the house she finds that the older girls have a boy acting like a pet, long story short, she (willingly?) decides to become a pet along with the boy.
Basically the gist is,
Girl enters house -> sees boy acting like pet -> in the end becomes a pet as well
Sorry, but its been awhile since i read this and its quite old (I think), and i can't give a lot of detail, and i may have messed up some details, so if you know of anything remotely similar please tell me.
Thanks for your time!