Kanoko Himemiya is the only reserved girl in a school full of delinquents and slackers. In contrast to her older sister Mayu whose fame is constantly rising, Kanoko, with her plain looks and personality, is destined to live a life of mediocrity. The only thing the sisters have in common is a unique butterfly-shaped birthmark on their thumbs. However, Kanoko catches the eye of Tsubame Yoshizawa—a ladies' man who enjoys painting girls' nails—and he insists on painting Konoko's as well, although his every advance is rejected.

When Kanoko finds herself being harassed by the paparazzi regarding her sister, Tsubame unexpectedly comes to her aid. As they make their getaway, their thumbs touch and memories of a past life rush through their minds. Tsubame explains the phenomena: following a double suicide, he and his lover have now have been reborn in the present, destined to search for their soulmate. Their only means of uncovering these memories is by pressing their butterfly-shaped birthmarks together, but the visions they see do not always match.

Believing Kanoko to be his destined lover, Tsubame wants her to be his girlfriend, but Kanoko has a strong suspicion that it is her sister that he is looking for. The vision Kanoko and Tsubame share begins to complicate itself as more people with the same birthmark appear, weaving a complex tale that binds a group of friends to a tragic past. With only faint glimpses into the events that happened centuries ago, they have to decide whether to pursue their star-crossed lovers or reject their own predetermined fates.