This is Meltlilith’s id_es skill.
During battle, she increases her attack rating. The longer a battle goes on for, the more her sadistic tendency increases, and she loses her cool. This skill is just one step away from turning her into a Berserker. The more she attacks, the stronger her attacks become, but on the other hand her defense capability decreases. A very effective skill in one-on-one battle, however in drawn out group battles or dungeon exploring it proves to be risky.