Chaos is one of the executives of the Secret Society who had suddenly and unexplainably lost his memories and became completely insane. However, his position in the organization was still held and Chaos entered the second Toshinden tournament under the orders to eliminate the traitor Gaia. When the Secret Society had fallen in its conclusion, Chaos had managed to survive somehow and participated in the third tournament.  During the events of the fourth tournament, Genma possesses the shield once carried by Chaos, indicating a high probability that he was killed by him.

For one year, Master Swordsman Eiji Shinjo has been haunted by the memory of his battle with the renegade champion, Gaia - a battle that was cut short by the forces of the malevolent syndicate known as "the organization." 
Denied victory, Eiji left the tournament followed by his opponents mocking laughter. Worse still, Eiji walked away no closer to finding his long lost brother, Sho. But now, a mysterious warrior is hunting down the champions of the previous tournament and using their own moves against them - and it looks like that person may be Sho. Who is this powerful new foe and who is his next target? 
Eiji and Kayin, his closest friend and greatest rival, struggle to unravel the mystery before they, too, join the ranks of the defeated. The answer lies at the heart of the Organization and its plans for world domination. At last, the ultimate battle between the greatest fighters in the world will be decided. But if Eiji loses, his friends - Ellis - may Die... 
(Source: AniDB)

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