Maou-sama Exchange!!

Hero Filina's party is on the brink of annihilation in the face of a powerful Demon Lord. The almighty demon proposes to spare their lives on one condition - that he may swap bodies with the hero for a year. Atty, a Priest and Filina's childhood friend, naturally objects to the proposal, but Filina agrees to the terms to protect her companions. Thus begins a new journey for the Demon Lord, naïve to the ways of the world, and the quirky group of adventurers, as they set out to vanquish the new Demon Lord once and for all...!!

(Source: MANGA Plus)