Ore ga Inmajutsu de Dorei Harem wo Tsukuru Hanashi

A man was summoned to another world inhabithed by angels, demons, humans and demi-humans. He was told by the demon-race to collect magical power, and the method of collection he chose was "rape"... What will become of the girls who fall into a slave training...? (Source: Syosetsuka ni Narou, translated)