The sequence begins when Nozomu Futami, the protagonist, returns to town where he grew up to attend classes and live with her aunt since her father has gotten a job as an astronomer in Hawaii, and Nozumu has preferred to stay in Japan.
His aunt is the custodian of a temple in which there is a stone according to local legend recalls the curse of twin sisters who fell in love the same man, and this not being able to choose for either died of grief becoming two small birds, and they say is the main reason the city has more twins than normal. And nozumo have to deal with the love of many twins, like the legend.