Events in Break Chance Memento center on the Amamiya family: brothers Natsume, Masaharu, and Shuuki.
Four years ago, Shuuki Amamiya’s world was turned upside-down upon the accidental death of his twin sister, Fuyuka, at just 12 years of age. Afterwards, their parents blamed Fuyuka’s death on Natsume, the eldest Amamiya brother, because he was the one who’d been with her when she died. Though the specific details behind Fuyuka’s death remained murky, at best, there was no going back. The Amamiya family would never be the same.
In the summer of 2012, after their parents go abroad temporarily for work, the three Amamiya brothers have to move into the dormitories of their private high school. One September morning, Shuuki happens upon the dead body of his older brother Masaharu, who was brutally murdered. Shortly afterward, an oddly-dressed stranger appears out of thin air and tells a grief-stricken Shuuki: “Do you want to bring your brother back? To fix your family relations? You can…if you learn to travel through time.”
Before he knows it, Shuuki is right in the middle of a plot far more sinister than he could have ever imagined. Soon enough, he finds that the key to traveling through time and stopping innocents from being killed lies in break chance mementos–items that are a link between the past, future, and present.