The Devil Arms are part of a sidequest in Tales of Symphonia. Upon completion the player will unlock the true powers of the weapons they receive completion. The weapon's power is based on the number of enemies the character has defeated over the course of the game making the Devil Arms the best weapons in the game. There is one for each character. The actual side-quest is easy, and doesn't make you go off the path a lot. The battle is the part that might take you a while.
In order to start the quest you must find the Evil Eye Chakram by destroying the Bacura in Toize Valley Mines. Take the lift down to the bottom floor to search the remains of the Bacura. You will receive the Evil Eye. When you get the chance, visit Flanoir and speak to a man named Abyssion. He will notice the Evil Eye and will give you Lloyd's Devil Arm Nebilim and the Nebilim key used to open the chests for the other Devil Arms.
- Evil Eye
Character: Collete This is necessary to start the quest. Search the remains of the Bacura in Toize Valley Mines.
Character: Lloyd You get this after speaking to Abyssion in Flanoir along with the Nebilim Key. You must have the Evil Eye.
Character: Genis In Altamira, sleep at the inn and go out at night. Go to the theater/casino. There will be a man selling it for 1000 Gald on the bridge. (Must have Fafnir)
- Soul Eater
Character: Kratos/Zelos Go to Triet and speak to two men talking about the Sand Worm. Outside of Triet on the World Map there is a glowing ring of light. Activate it to battle the Sand Worm to get this Devil Arm.
Character: Kratos/Zelos You will find the chest for this in the Garrochia Forest. Use the light power of the Sorceror's Ring to reveal it in some bushes.
- Gates of Hell
Character: Sheena Talk to a Gnome at Altessa's House after completing the Earth Temple. Go back to the Earth Temple where there will be no more Gnomes blocking your way. Find the black chest and open it.
Character: Presea In the second part of Latheon Gorge, on the left side of one of the hills there will be a chest.
Character: Regal Go to Welgaia and at the main area (with all the building) head into the large one and go to your left. You will see the next chest.
- Heart of Chaos
Character: Raine You must get this one after all the others. Talk to Abyssion in Flanoir and head to Hakonesia Peak and speak with Koton for the final weapon.
 The End of the Story
To finish the Devils Arms sidequest and unlock their true potential, you must travel to the Temple of Darkness. There, you will fight one of the strongest bosses in the game (a lot stronger than Mithos) It's a monster called Abyssion. By defeating him, you will unlock the power of the Devil Arms.
 The Battle
After you have collected all of the Devil Arms meet Abyssion in the Temple of Darkness. Go down to the altar to trigger a scene. Here you will find out that Abyssion has had one of the restricted dark magic books all along, which is what he uses to turn into his demon form.
This is the hardest boss of the game. He has 120,000 HP on Normal Mode and very high attack/defense with no weaknesses or resistance. His techs include the most powerful ones from every character in the game including Indignation, Meteor Storm, Victory Light Spear, etc. He is very fast and hard to evade. His spell casting time is very short.
In order to defeat Abyssion it would be a good idea if your party is over level 70 with the best equipment and skills possible. Raine is necessary with her great healing and stat boosting spells. Be sure to have an inventory of Life Bottles and all kinds of gels. Skills such as Speed Cast (level 3) and Save Spell (level 4) will make healing faster and almost impossible to be interrupted. This is also useful if you are using Genis. An additional meleer such as Zelos or Kratos also helps. If you are under level 70 then a good idea would be to use an All-Divide. The battle will last long so any mistakes will make you start all over again.
After you defeat him, the true power of the Devil Arms are unlocked and Presea will get the Empty Soul title. The true power of the Devil Arms are to gain 1 attack point for everything you kill. Say you kill two thousand enemies with Lloyd's weapon. Their attack power will increase by 2000.
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