Yukito's school life is thrown into chaos following the suspicious death of a popular student and the sudden disappearance of his friend, Kotomi. As he investigates, he discovers that a social outcast named Mamiya is obsessed with a nihilistic philosophy called "Endsky," believing the universe must reach a definitive end. Yukito eventually tracks Mamiya to a derelict pool to rescue Kotomi from the delusional youth's grasp.