Following the loss of his parents, Yuuto Amakawa resides a mundane life in the urban area, with his sole setback being his allergy to cats, while attending school with his neighbor, Rinko. However, his ordinary life is disrupted on his sixteenth birthday when an Ayakashi, a paranormal being, assaults him for the misdemeanors of his forefathers. Fortunately, Heimari, an enigmatic feline-humanoid warrior with a sword, comes to his rescue and reveals to Yuuto that he hails from a lineage of demon-hunters. Henceforth, she pledges to safeguard him since the amulet that had kept him hidden from the supernatural forces has lost its potency. Omamori Himari outlines Yuuto's encounters with different entities from the paranormal realm, accompanied by the arrival of an increasing number of women at his doorstep, each harbouring their own sinister aspirations. Will Yuuto acclimatize to his newfound "stimulating" vicinity, or will the apparitions of his forefather's past catch up with him?