Shureishi

Eiji Ando is taking over his family business of being a "Shureishi" or simply an exorcist. Unbeknownst to him, the REAL purpose of his family tradition is to use spirits (which they keep as 'pets') to take over women so that the shureishi can mate and produce offspring! What happens is the female characters get possessed by the spirits and when they leave the body, Eiji needs to have sex with them in order to completely rid her of the bad aura (or supernatural residue).

(Source: MangaHelpers)