Originally, the bunny had a big, bulky muscular body. I think it would be interesting if, when he became (possessed) she, she kept his muscular build just like how she kept his bunny ears.
Soo there are about 3 possible endings for this bunny spirit? It dies and it's female host becomes a requiring character that now has spiritual powers due to her possesion. It's gets enslaved to serve the MC. Or just dies together its host.