In ancient times, some witches married their familiars, who had taken human form, giving birth to a lineage of ogres. One such ogre is Morihito Otogi, who while appearing completely human, still 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 go to the Witches' Holy Land to train and part ways with Morihito.

Years later, just before Morihito's first year of high school, Nico returns home with one goal in mind: 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 with both of Morihito's parents elsewhere. While reluctant at first, Morihito accepts his new role, determined to help Nico seamlessly fit back in with human society and protect her from fated disaster.