Maou-sama no Kinyoubi

The Demon Lord, who was once defeated in battle by a hero, was suddenly transported from the demon world to modern-day Japan due to a runaway spell she cast at the end of the battle. Having efficiently recovered most of the magical power she had lost in the previous battle 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, by chance, she came across a back alley in a busy downtown area and ended up helping a girl who was being harassed by several men. As a reward for helping her, she was taken to a cozy oden restaurant... The serious and rigid "Demon Lord" discovers truly delicious food and drinks, and friends to share them with after work. (Source: Tonari no Young Jump, translated)