I don't know for sure, but I think it's just a couple missions before the end. You have a choice to either fight Cinder Carla (siding with Ayre) or to fight the corps (siding with Carla). I sided with Carla, which made Ayre the final boss, and the fight was godawful. My understanding is that there are maybe more endings with NG+, but I'm trying to muster up the will to bother even turning the game on again after how atrocious the Ayre fight was.