In ancient times, certain witches married their familiars who had assumed human form, thereby creating a lineage of ogres. Morihito Otogi is one such ogre; although he appears entirely human, he retains the inhuman strength of his bloodline. Nico Wakatsuki is a young witch and Morihito's childhood friend, but as part of her education, she had to travel to the Witches' Holy Land for training, which meant parting ways with Morihito. Years later, just before Morihito's first year of high school, Nico returns home with a single goal: to claim him as her familiar. While most witches choose a cat or a bat, Nico has her heart set on Morihito in more ways than one. Although seemingly oblivious to her true feelings, Morihito and Nico end up living together under the same roof while both of Morihito's parents are elsewhere. Initially reluctant, Morihito accepts his new role, determined to help Nico seamlessly reintegrate into human society and protect her from a fated disaster.