Teisou Gyakuten Sekai no Onsen de, Sansuke Yaru Koto ni Narimashita

A young man who has lost his memories finds himself in a world where women outnumber men 100:1 and traditional gender roles are reversed. There, he's taken in by Misago, the heir to a hot spring inn. She gives him the name Hisui, and he begins living at the inn. Of course, he can't keep living there without contributing anything forever. So the job he's given is... to work as a sansuke, a male bath attendant responsible for washing female guests' backs. Hisui quickly adapts to this gender-reversed world and settles into a happy life at the hot spring inn. Meanwhile, the girls who find themselves constantly caught up in his antics gradually begin falling for him. (Source; Kill Time Communication, translated)