In the pitch-black, mysterious underground sea, with its enigmatic islands and terrifying deformed monsters, humans are not the protagonists of this cursed place—madness and death are.

The humble prayers to those things beneath the sea only cause the wretches to linger in the darkness, gradually becoming twisted. If one wishes to reclaim the former glory of humanity, the only way is to board a steamship and charge into the undersea with a resolve to die!