Kitone (Summer) is a magic damage dealer that uses a mix of offensive spells from main job, and slash attacks from sub jobs, making her good against enemies that are weak to magic or slash attacks. Compared to units like Howlet or other mages, Kitone is more of a bruiser/fighter since she has more defensive options. Her spirit and slash penetration plus lowering enemy's fire resist abilities can help her handle 2 different attack types somewhat effectively.
Unfortunately, her Rune Knight abilities may be a bit outdated since they come with drawbacks like short range, damage, or high ap. And while she does have good defensive abilities, she needs her EX upgraded, which can end up making her costly on top of being a limited time unit.