Sister ∞

As stated in the description, the improved version of the Sailor 0. Ironically, they also added to it a flaw, which is apparent from her skill set: she has a three-strike attack called Drei Blade and can restore her HP with Refrag, but she also has one called Trip&Fall that causes her to waste her turn due to tripping and landing face-first on the floor. Therefore, and despite her much higher stats, the Sister ∞ is an enemy that shouldn't give problems to anyone, as she only has one real offensive skill.