Mary was the supreme ruler of the Demon Empire, whose three-year reign ended in a violent coup after she refused to rule with blood and fear, showing instead a forbidden compassion for humans and the other races. Now exiled, she goes into hiding amongst the very people she had sacrificed her throne for.

Accompanied only by her loyal familiar, Gustav, former beast of the underworld turned regular house cat, Mary sets out to live the peaceful life she has always dreamed of. However, blending in as a human does not come as easily as she imagined.

Her demonic abilities turn simple jobs into disasters, and her sheltered upbringing as royalty threatens to expose her lack of common social etiquette.

Follow Mary as she navigates commoner life by day, forming friendships, and by night, secretly taking up her blade to defend the people from the remnants of her former empire, while also carrying out undercover missions to help better the lives of her new friends and family.