Sixteen-year-old Emma finally arrives at the capital city Hawk Eye after escaping from being held captive for her entire life. But as soon as she arrives, every man in the city, including the king, falls madly in love with her. She is about to be forced into marriage, but is saved by a sorcerer. The sorcerer identifies himself as Shion, one of the youngest and most talented in the nation. They have met before, but Emma has no recollection.
Shion explains to Emma that she is cursed with the Ekidona, a mysterious magic that happens every 500 years where a girl is born with her heart packed with such powerful dark magic that it has the potential to destroy the world. With such power, one could rule the world, and Shion explains to Emma that people are going to try and hunt her down to get her heart. However, Emma is told that there exists a ritual that will rid her of the Ekidona curse but doing so will require a long and arduous process. The first of that being Emma and Shion will have to marry each other...

The Shirakiin house's daughter, Shirakiin Riricho, who has a complex about being unable to live independently and unprotected, feels the need to move out and live on her own under the condition of residing in the mansion named "Ayakashi Kan." In this mansion, only those who have cleared a very strict examination could reside in it, and for each resident, they are accompanied with one agent of the Secret Service (S.S.). Although Riricho has rejected the company of the S.S., while residing in the mansion she finds out that the agent dedicated to protecting her is actually the Fox Spirit whom she previously rescued.