The Saint of Betrayal

Inaba Mari was summoned to save the world. She was welcomed into the kingdom as a holy maiden destined to defeat the Demon King, but a cruel fate awaited her. Marked with a slave tattoo and suffering in despair, Mari was guided by the ghosts of girls who had been summoned before her. Mari met the Demon King and swore to serve him. Having fallen as a member of the demon race, Mari abandoned her weak girl's body, obtained a strong man's body, and slaughtered the king and priests. Ten years later. A prince, the sole survivor of the kingdom, appeared before Mari, who had been living peacefully in the demon realm.