Humanity is plagued with attacks by a race of sea mutants dedicated to eradicating mankind. Our last hope is the Blue Submarine No. 6 and her crew, made up of the best personnel available as they fight for the fate of all mankind.

Tetsu drifts in the open sea. As his life flashes before him, he begins to black out. But when he comes to, he finds himself resting on the hull of a half-sunken ship. His savior is one of the enemies.