On her 16th birthday, Himari Momochi receives a letter stating she has inherited a mansion called the Momochi House. Having been raised in an orphanage, this mansion is the only thing left of her real family, so Himari pays no mind to the rumors that it may be haunted. Upon entering it, she meets Aoi Nanamori and his companions, Ise and Yukari, who all seem to be squatting in her new home. Although they warn her to leave the house, Himari vows to be the one to make them leave instead.

But soon, she is attacked by youkai and finds out that the house sits in the space between the world of the living and the spirit realm. Even more surprising, Aoi was chosen to be the guardian of the house—a position originally meant for Himari. But this great power came with an awful price: Aoi can never leave the mansion, and his existence in the human world has been erased. Ignoring his pleas for her to leave the mansion, Himari promises to help Aoi break the housebound curse as she begins living under the same roof as him.