RRose is very important for the new mission. You have 3 turns for the last boss to deals as much damages as you can before he overkill you. And he has TOO MUCH HP. Close to 10M I guess. And your teams are already dead from the previous fights.
Counter+Crit team works well for the first fight. Second fight is very hard and the last one needs all your best Crit-Nuke-React-Weakness-Damage-Boost-and-all-you-can.

I really need the RG Gacha and it's 2 Centies.