Egg

These monsters are the minions summoned by Zzx_Ru, and while they have a rather pathetic HP and stats, this is offset by the fact that they are nigh immune to all forms of attack. This might not seem as much, but given their sole form attack, it will be a great of trouble during said battle: their attack is called Suicide Bomber, in which they self-destruct to cause a tremendous amount of damage to all characters around of themselves, and if they manage to reach your Reyvateil, you can be sure that this attack will instantly kill her. And to make matters worse, Zzx_Ru can continue producing more of these as much as it wants.

Therefore, the best you can do is trying to destroy them and keep them off your Reyvateil while you continue fighting Zzx_Ru, so you should try to end the battle as fast as possible.