Saikyou Ninja no Boku ga Maou no Musume-tachi no Maid ni Natta Ken The Strongest Ninja Became the Maid of the Demon King's Daughters.

Synopsis

Hikage, a skilled ninja, joins forces with one of the demon king candidates and helps him become a demon king as a maid? A harem love comedy with three demon king candidate sisters! (Source: COMICSMART, translated)