Ao no 6-gou

In the near future the oceans have risen, causing all land at sea level to be flooded.

With the expansion of the oceans, humanity has found a new enemy in Jung Zorndyke. A war has erupted between the surface dwellers and the sea dwellers, and mankind is placing all of its hopes in the new vessel Blue Submarine No. 6 and her crew.

Kino Mayumi is a young, devoted pilot.

It is her current mission to convince Hayami Tetsu to rejoin the Blue Fleet.

However, he refuses and angers her, so she leaves.

Later, however, the two meet again under more dire circumstances and start to work together.