-Do the following to easily defeat Chaos in the final bonus chapter. You must be at least level 100. Before entering the battle, make sure you have accessories that grant bonuses most of the time (in danger of losing are extremely effective), and at least 30% boost to attacks and 5% to defense. A Phoenix Down is also recommended. Equip the summon "Magic Pot" (auto or manual). In abilities, make sure you have an attack that covers long distance and short distance in the air. Ground does not matter, but you should have at least one close range attack. Make sure you have "Exp To Health", "Riposte", "Counter Attack", and "First Strike" (recommended). Try to optimize equipment if you have not already done so. Make sure you can avoid any and all health attacks. Timing is crucial for all of them; however, most are easy to avoid. You should dodge "Divine Judgment" slightly earlier to give you time to launch a health attack. As soon as the battle begins, move to the top of the battlefield by dodging and jumping. Once there, Chaos should only use "Divine Judgment" and close range attacks. When he charges you to use the close range attacks, block and hit him with a Brave attack that launches him away from you, but not into a wall. Downward works best as he will repeat his charge. Block the charge, and repeat. Break him once, block his charge, perform a health attack, then refill Bravery for the first kill. Repeat this for his second form; however, be aware that he now uses summons and teleportation attacks. With a little luck you should still be able to copy the earlier technique without using your summon. The third form is more difficult. He will pound you with Brave attacks. The other technique will not work because he now teleports to do close range attacks 80% of the time. If he pummels you to 9999 Brave, you are probably going to die. Health attack to stop your almost guaranteed break, then perform Mimic using your summon. For the last hit, wait until he uses his "Oblivion-Beam-Of-Doom" or "Divine Judgment". If you are skilled with your timing and dodging, blast him, and you are finished. Note - This was done with Squall with Aerial Circle and Rough Divide in the air and Fate Circle on the ground with all the previous mentioned abilities. Brave attacks do not really matter (using only two of them; one that launches the enemies straight down in one hit and the other with rapid fire straight down - ground Brave attacks were useless). With Rough Divide, you can stop Chaos' "Oblivion" attack, and Aerial Circle for "Divine Judgment". You just have to dodge any other attacks.
-Before fighting Chaos, make a Valor Resin (Initial Brave +200%), an Arcane Resin (Initial Ex Force 100%), and two Valor Incense (Initial Brave +100%). These will break if you lose, but will last all three battles. The Valor Resin will multiply your Initial Brave by 5x. Set Alexander as your summon, and activate it in the third round; go into Ex mode after you activate it. Land your HP attack and EX Burst, and he will never get a chance to use "Utter Chaos".