Lee Jieun is a noble girl who is terrible at magic, as her attempts usually result in an explosion. She is nicknamed "Jieun the Zero" by her classmates, due to the inability to use any of the four magic elements. Early in the school year at the Kirin Academy of Magic, the second year students perform a special ritual where they summon their familiar, which serves as their eternal protector and partner. Usually, this 'familiar' is some type of magical creature, but instead- Jieun summons Byun Baekhyun, an ordinary teenage boy from Korea, leaving her totally humiliated.

Due to the sacredness of the ritual, Jieun reluctantly accepts Baekhyun as her familiar, but proceeds to treat him as any other familiar, but only worse- making him wash her clothes, sleep on a bed of hay, and whipping him with a riding crop for little or no reason. 

On just the first day, Baekhyun tries to find a way to get back to Korea, but only ending up to realizing that the place he's currently in has two moons. One moon as the Earth and the other as just the plain old moon. Until he finds a way back to his home planet, he's stuck in the situation as Jieun the Zero's familiar.