Toriko: Eyes of a Rapist.

A dangerous lunatic going around breaking into the apartments of various women and brutally raping and killing them while wearing a black outfit and black bondage mask. One night he breaks into the apartment of a care worker and rapes her. He doesn't kill her though as he finds that he falls in love with her. So instead,he returns on different nights and rapes her time and time again...pretty rough life for her considering she was gang-raped when she was a schoolgirl (shown in flashbacks). She falls in love with the detective investigating the case,but the rapist is still on the loose.