Eighteen Years, to the Sea (1979)

Kei, a dedicated honor student, and Atsuo, his carefree counterpart, find themselves in the same summer school class. Their contrasting personalities spark an unexpected bond. One day, they venture to the beach and encounter a thrilling contest between a fellow student and a local tough guy, testing their underwater breath-holding skills. Caught up in the adrenaline of the moment, Kei and Atsuo impulsively decide to join the challenge, leading them into a whirlwind of competition and camaraderie.