In the world of Pentagaia, there is a castle floating in the sky where secrets are said to sleep. The lords of five kingdoms — each from a different world — have gathered at this Celestial Castle in hopes of finding a way back to where they came from. Then a sixth seeker appears in the castle without explanation, and with her arrival comes a mysterious dungeon gate. She has no memory, and the only thing she knows is that she must go to the abyss. She enters the underground gate and begins the journey through the depths.