Saikyou Maou wa Musou Shiteta no ni ~Nyotaika Kaijo no Kagi wa Hitodasuke no Tabi deshita~

Dinato, once feared as the mightiest Demon King, was cursed by an item belonging to Annie, the female hero he defeated. Transformed into the body of a beautiful girl, Dinato's troubles only grew when Annie was revived as a gyaru—and due to the curse, Dinato is unable to defy her! Stripped of most of his powers and now targeted by his former monstrous minions, Dinato is brought to his knees by this harsh reality. Amidst his struggles, Annie reveals the only way to return to his original form: a journey of "helping people" by defeating monsters that threaten humanity—a task utterly unbecoming of a Demon King...