Our War (Bokutachi no Sensou)

Kenta (Mirai Moriyama), who accidentally slips back in time from 2006 to 1944 shortly after seeing a sudden lightning flash while surfing. Soon he finds he has mysteriously traded places with a young soldier, Goichi (also Moriyama), who was doing flight training over the same area of the sea where Kenta was surfing.

Kenta, as a soldier, is then sent to an Imperial Japanese Navy base, where he is assigned to be a pilot for one of the manned torpedoes called Kaiten.