Two families are tied together by a curse. Every 100 years, one person from each family must share the same fate for exactly one year. The pair will be subjected to twelve misfortunes, where one will get hurt while the other must sustain their injuries in return.

When Kagura Izumi was seven, his parents died in an accident. Since then, he has been living an ordinary life. Until the day of his seventeenth birthday, when he meets a mysterious transfer student, Ichijyou Chihaya. However, this fateful encounter between them is only the start of their intertwined fate. For the next year, the two of them will be forced to face 12 misfortunes on the 13th of every month, a curse that has never left any previous pair alive.