Kin to mahó to Wooser to (S01E10)

Every night, Wooser is visited by a mysterious girl in his dreams, who says, "Hero, please save my world!" The insomnia makes him very angry, and he leads an undead army into the world of dreams and destroys it. The girl was the Queen of this world. "The shorter the sadness you must endure, the better," Wooser whispers, as he goes back to his hand-to-mouth life. (Crunchyroll)