Saike Kuzushiro
A boy who has no objective in life, until the moment when he accidentally discovers he can get back in time to the morning of the same day if he drowns in the Mogura pond.
Saike is a middle-school student whose best friend was killed by a truck. Saike tried to drown himself in the nearby lake, and that led to him learn about his new-found power.
His power is to drown himself in the lake to return to 7:00 of that morning.
Mangaography