Tsukuyomi. Gameplay she has some issues, and she tends to be one of the most common fights i come in progress to or see abandoned. She's just murder on newbies, to the point where you should watch a video if you are a new healer on it, or switch to dps or tank. She's also designed to prevent carries, as lunacy acts as a death check, dooming the raid if enough people are on the floor. Thematically she's great, though.