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

Synopsis:

Dinato, who was once regarded as the most powerful Demon King, fell victim to a curse cast by Annie, the heroine he had overcome. Changed into the shape of an attractive girl, Dinato's difficulties intensified when Annie was brought back to life as a gyaru—and because of the curse, Dinato cannot oppose her! Deprived of most of his abilities and now pursued by his old horrific followers, Dinato finds himself weakened by this cruel truth. In the midst of his challenges, Annie discloses the sole method for him to regain his former self: embarking on a quest of "assisting others" by vanquishing monsters that pose a threat to mankind—a mission completely uncharacteristic of a Demon King. . .