Zero-1 Sentai

(from ebookjapan):

In just four years, he destroyed 13 naval ports, 6 naval vessels, 1 aircraft carrier, 1 battleship, and 25 submarines, and was known as the number zero one of the Imperial Japanese Navy. The legendary man died in May 1950, three months before the end of the war, in an attack by U.S. forces.

As time goes by, Akira, a young boy who admires his uncle Number Zero One, runs away from home to become a frogman, amidst the worry of his mother and older brother, and embarks on a thorny and perilous path...