The story is set in a town called Sakurada, where almost half the population possess some form of special powers. The story centers on two high school students. Asai Kei has the ability to perfectly remember anything he sees and hears, while Haruki Misora can turn back or "reset" time for a maximum of three days.
Both students are members of their school's "Service Club," which their town's administration bureau uses to observe people with powers and protect the peace. By using their powers together (Kei can remember things even when time has been reset), they solve cases for the club. Kei learns of the "MacGuffin" stone, which looks like a worthless black stone, but in reality will turn out to be the stone upon which the existence of Sakurada will hinge on.