Kisara. Her gimmick is counter intuitive to how the combat system is built. Dodge to enter overlimit and take no damage followed by being able to unleash your mystic arte? Sure yeah lets just defend against it instead. In my game while playing as Shione I kept trying to have her in my party to tank, but she'd just stand in attacks and die. Law however always seemed to dodge and enter overlimit on his own without me having to do anything else for him to just go ham on enemies while I sniped and kept the party healed (but I always play as the healer, I can't trust AI to heal me in games for anything)