Maou-sama no Kinyoubi

Beaten by a hero, a Demon Lord casts one last spell that misfires and drops her out of the demon world and into present-day Japan. Modern cooking proves an efficient way to rebuild the magic she lost, and she eventually returns to rule her own realm, though she keeps slipping back for convenience store meals. During one such trip she wanders into a downtown alley and steps in when several men are hassling a young woman. The rescue earns her an invitation to a welcoming oden shop, where the stiff, humorless ruler finds good food, good drink, and company to share them with.