Instructions
Choose to use a character who both has high stats and who you are most comfortable playing with.
Begin the battle with fully charged EX bars to help take the advantage early on.
Use support abilities and summons to increase your character's defenses or decrease Chaos's damage at the start of each new fight. Chaos does very powerful attacks that can likely kill your character in one hit if you are not playing defensively enough.
Dodge Chaos's attacks as often as possible. Follow up with a strong attack to take advantage of the fact that Chaos will be vulnerable after you successfully dodge one of his attacks.
Defeat Chaos three times in a row to kill him. He will progressively get harder with each new fight, dealing more damage and using new abilities. Save your strongest abilities and summon spells for the final fight.