Well, you know how it does this move that applies a stacking "guilt" debuff to everyone (including the enemies)? If it ever reaches 10 stacks on anyone, they die at the end of the turn, and you can transfer stacks to others by attacking or supporting them, so you'd have to try and ensure none of your party members accumulate too much guilt while stacking it on the enemy.
Gotta say though, it's pretty impressive you made it that far. Perhaps I should make an achievement for beating it with pure damage...