Jo,die KI deiner Mitstreiter ist teilweise echt unter aller Sau,ich glaube das hängt auch von der Intelligenz ab,naja ich hab am Endgegner selber aufgegeben.Bei Gamefaqs habe ich einen Trick gefunden,keine Ahnung ob du ihn anwenden kannst:

Oh yes, there's a REALLY EASY way to beat him, if you have Precis and
Chisato, put them in the battle, both with the shield 'Algol' equipped.
That is the legendary Medusa sheild or something, so it can stone any
enemy (including bosses). But the person wielding the shield usually has
to parry with it, and the boss has to be looking directly at the shield
when it's being used to parry (you don't know if the boss is looking or
not). But enemies usually are "stoned" (actually, they just die because
of this stoning) when the wearer of the shield parries with it (not the
Combat Skill Parry, just blocking). This works on Indalecio (Limiter
Off) so you might want to try it to kill him easily, or should I say
"quickly?"