The CPU has two exterior components, the Attacker (on top) and the Defender (on the bottom). Like other three-part bosses, the CPU will restore both sub-parts if they are destroyed. However, the CPU will also kill off two party members when this happens, so avoid doing so at all costs! The CPU also casts Wall on itself, making things even tougher. The Defender's healing is very powerful, so you should destroy it, and leave the Attacker in place. The Attacker will repeatedly use Maser, which deals 10% of each Character's max HP in damage.
Because the CPU has Wall and needs to be hit without hitting the Attacker, you have limited options. The Sylph summon is effective and should keep up with the damage from Maser, but Rosa and FuSoYa have no safe method of magical offense. Bersk won't work either, since the Attacker will soon die. You will be relying mainly on Cecil and Edge to deal damage here, and you may want to Throw Shuriken or spare Weapons at the CPU.
Because the CPU has Wall and needs to be hit without hitting the Attacker, you have limited options. The Sylph summon is effective and should keep up with the damage from Maser, but Rosa and FuSoYa have no safe method of magical offense. Bersk won't work either, since the Attacker will soon die. You will be relying mainly on Cecil and Edge to deal damage here, and you may want to Throw Shuriken or spare Weapons at the CPU.