Kratos Aurion is a pivotal character in Tales of Symphonia. He first introduces himself as a traveling mercenary and saves Lloyd, Genis, and Colette from an attacking group of desians, later revealed to be the Renegades. Kratos is then hired by Colette's grandmother, Phaidra, to protect the Chosen on the journey of World Regeneration. It was during the course of this journey that the group discovered that Kratos was an angel of Cruxis, an organization that has overseen the world for 4000 years. Kratos betrayed the group at the Tower of Salvation, swiftly defeating Lloyd and the group in order to deliver the Chosen, Colette, as the new body for the goddess Martel. Despite his efforts, the incapacitated Colette escapes with the help of the Renegades. He then leaves the party.
After the betrayal, Kratos returned to Cruxis. As an agent of Cruxis, he was ordered to keep track of the Chosen. Because of this, he runs in with Lloyd and his friends in several encounters, each ending with conflict. Despite acting on orders of Cruxis, he covertly gives Lloyd advice on their next destination. Kratos later rejoins the group during the Renegade Kharlan Tree incident to help them shut down the Iselia Ranch generator. After stopping the tree from running amok, Kratos leaves the party again, this time giving advice to Lloyd on how to cure Colette's illness. It was then that Lloyd learned that Kratos was one of the heroes that ended the Great Kharlan War 4000 years ago. Kratos confronts Lloyd a second time in the Tower of Salvation, confirming that information. After curing Colette's illness, Kratos reveals himself to be Lloyd's father, but their meeting is abruptly interrupted by Mithos.
Kratos' intentions become more apparent after he reveals that he was collecting materials to forge the Ring of the Pact, which allows the user to wield the Eternal Sword unrestricted. In order to wield the sword, Kratos must be defeated to break Origin's seal and release the summon spirit that created the sword. Kratos' final confrontation with Lloyd in Torrent Forest served as both a test and a chance for redemption. The fight ends with Lloyd's victory and Kratos gravely wounded. Depending on the player's choice, Kratos may accompany Lloyd and his party to the final battle. In the end, Kratos chooses to remain on Derris Karlan in order to find a place where half elves can live. Kratos makes a minor appearance in Tales of Symphonia: Dawn of the New World, saying a final farewell to his friend Yuan Kafei before Derris Kharlan goes beyond communication range. His ultimate fate is unknown.
Kratos is a versatile fighter, able to use both melee artes and spells. Although slow in ground combat, Kratos' attacks are fairly powerful. However, most of Kratos' strike artes consists of master and arcane artes, leaving few starting base artes. Like Lloyd, he has the base artes Demon Fang and Sonic Thrust and their master arte variations, Double Demon Fang/Fierced Demon Fang, and Hurricane Thrust/Super Sonic Thrust.
However, their similarities end there. Kratos' artes diverges to Light Spear and its variants Victory Light Spear/Light Spear Cannon, which involves a spiraling upward cut on surrounding enemies. His most popular yet dangerous move is his Lightning Blade arte and its variant Super Lightning Blade. Both involves him thrusting his sword into the enemy and striking them with powerful lightning and wind pressure. His other arcane artes are Demon Spear, which is a combination of Demon Fang and Light Spear, Hell Pyre involves him jumping up in the air and rain down fireballs. Guardian Field creates a field of rising energy that damages surrounding enemies.
Kratos' spells are marginally weaker than Genis, but are still useful in many situations. Like Genis, Kratos has the novice spells Fireball, Wind Blade, and Stone Blast, and Raine's healing arte First Aid. His mid level spells consists of Eruption, Air Thrust, Thunder Blade, Grave, Healing Wind, and Healing Stream. Kratos only has one angelic spell, Judgment, which rains down the rays of judgment to deal heavy damage to enemies. His mystic arte, Shining Bind, creates a field of light that binds and floats the opponent ending with heavy pillars of striking light that deals massive damage to all enemies caught in the attack.
Kratos' ability to use both strike artes and spells allows him to pull off long combos using the spell cancel method, which allows him to continue his attacks as long as he cancels a spell in mid attack. This also allows him to adapt to many situations.
Note: Kratos does not have Guardian Field or Shining Bind in the Nintendo Gamecube version of Tales of Symphonia, but receives them in subsequent appearances. Kratos also makes a cameo boss appearance in Tales of Vesperia with a majority of artes removed. In this appearance, artes such as Hurricane Thrust, Super Sonic Thrust, Demon Spear, Light Spear Cannon, Victory Light Spear, and all his spells with the exception of First Aid are removed. Some game mechanics have been altered, such as Lightning Blade and Super Lightning Blade gaining paralysis infliction and Guardian Field healing a small portion of health.
In the past, Kratos was Mithos' master and taught him how to fight, later becoming a close companion and a friend. Kratos also had close ties with Yuan Kafei, another companion who was traveling with Mithos. Four thousand years after the Great Karlan War, Kratos came down to the earth to escape from Cruxis and fell in love with Anna, a prisoner of a human ranch. They later concieved a child, who later became Lloyd Irving. Kratos and Anna fled the desians with Lloyd but ended with Anna's death. Heart broken, Kratos returned to Cruxis and was reunited with Lloyd sixteen years after. Their relationship started out bitter with Kratos cricizing Lloyd's fighting techniques and Lloyd seeing him as an arrogant jerk. However, they value each other as allies and Kratos often trains Lloyd to perfect his twin blades style. Even after his betrayal, Lloyd still believes in him and they later reconcile as father and son.