-( Story related, cannot be missed )-
Boss: Anamnesis
Boss: Bourbaki x 5 (with smaller health bars and their combined health forming the boss bar)
The fight against Anamnesis, for me, was one-sided with Nanana. She kept a combo up and kept her range, not allowing the Revenant a chance to get close enough to hit me. However, about a third through, she gave up when Sen joined the party and her collective minions appeared instead. If you've dealt with them prior to this with little difficulty, it is the exact same, only without an actual Revenant among them (in appearance; there is in fact one that you can get a Torment from).