The mechanics of this event are interesting. Character limiters, side missions, escalation... seems fun.

Though it does annoy me that you have to use a key to do EVERY fight, not just new fights. Why do I need to use a key to open a battle that already open? They could have just made it so that repeat runs award no additional medals unless it's from a previously uncompleted side mission so that you can't farm the lower ranks. It's already going to lock those characters for that run anyway so why make it more tedious then it has to be?