Tactics Ogre Reborn - Tips for the final boss of the main story

!So, I reached what I believe is the final phase of the final boss of Tactics Ogre Reborn. The problem is: I'm having a really difficult time with it. !<

!First phase goes fine. I have little problem with that. But the second phase, with the massive health pool of the boss and constant party wide damage, has become a problem. My attacks do very little damage, even when the boss is suffering from debuffs such as Breached and my units have collected buffs, and I struggle to even keep my units alive.!<

!So, I'd appreciate any tips you guys have regarding that boss. For reference, my team currently has 2 Warriors (one being Denam), one archer, one swordmaster, one wizard, Canopus, two clerics, a dragoon, a terror knight, a knight and a white knight.!<

!I have a save just before the final dungeon, so I can get out and train more units if needed.!<