Maousama no Kinyoubi

The Demon Lord is defeated in battle by the hero but suddenly transported from the demon world to modern-day Japan due to a runaway spell she had cast. After discovering she can efficiently recover most of her magical power by consuming modern food, the Demon Lord returns to the Demon World once again. Despite reigning over the demon world as the Demon Lord, she frequently makes secret visits to Japan, spending her days eating easily obtainable convenience store food. One day, she happens upon a back alley in a busy downtown area where she ends up helping a girl getting harassed by several men. As a reward for helping her, the Demon Lord is taken to a cozy oden restaurant... The serious and strait-laced Demon Lord discovers truly delicious food and drinks, as well as the friends with whom to share them...

(Source: Shueisha, translated)