When her father, a priest, left Japan for Eastern Europe, Yui Komori went to live with distant relatives whom she had never met before. She's spent a lot of time with the Sakamaki brothers but knows little about the history that caused their rift. However, as she becomes more involved with one of the brothers, she learns about the family's complicated history.
The brothers are related through Tougo Sakamaki—also known as Karlheinz—who had three wives. Shuu and Reiji are Beatrice's sons, Ayato, Kanato, and Laito are Cordelia's sons, and Subaru is Christa's son. The wives fought for Karlheinz's favor, and their children suffered as a result. Yui is particularly affected by stories about Cordelia, despite not knowing why.
Unbeknownst to Yui, she carries a secret within her body that explains her delicious blood's allure to vampires and her familial ties to the Sakamakis.
