After regaining consciousness, Yui Furukawa realizes that the calendar reads July 13—a day she has never lived before. Nevertheless, she chooses to spend her summer break with the other members of the Astronomy Club at Nagisa Hanamiya"s ancestral villa. The residence and its environs boast a storied past; Nagisa"s great‑grandmother, a distinguished scientist, once pioneered technology at the nearby defense factory.
While the club enjoys a beach outing, an abrupt storm cuts their plans short. With no better option, they seek refuge inside the derelict plant, eventually uncovering a concealed subterranean bunker. Inside, they may find evidence of an extraordinary link to a vanished future that could reshape their understanding of time and destiny, and guide them toward a destiny they never imagined today.