Marle and the Labyrinth of the Dark Sea / マーレと黒き海の迷宮

Marle has been known as one of the archmagicians since she defeated
a dragon and saved the country from its threat, despite her younger age.
Now she goes from one mystic place to another out of her keen curiosity.

One of these days, she overhears that an undersea historical site has been discovered
near an island called Isora isle. In search of new spells, she soon heads to the place.
Upon arriving, however, she finds that the site is rather a labyrinth inhabited
by new types of monsters that weaken human's power and increase desires...