From MangaHelpers:

Midori is a young lady from a good family, and she should never be caught inside a convenience store. However, when she's really hungry, she craves convenience store food. She sneaks into the store with her face covered, to make sure she isn't spotted by classmates, and then brings the food home to remix in a meal of her own creation. She loves this convenience-store-gourmet style, but is afraid that she will one day be found out!