Chaos  

, カオス

Chaos is an entity mutated by the Chaos Emeralds, which act as guardians for their species and protect the Master Emerald. They are water-like beings that can manipulate their bodies to stretch limbs or liquefy themselves. Without any emeralds, they are known as Chaos 0 but with each emerald absorbed, they transform into a more powerful form named after the number of emeralds until becoming "Perfect Chaos" with all seven emeralds. After the Echidna tribe attempted to steal the emeralds and harmed various Chao, Chaos absorbed the negative energy from the emeralds and became Perfect Chaos, causing chaos until being sealed inside the Master Emerald with Tikal. Thousands of years later, it was released in Sonic Adventure so Dr. Eggman could use it to conquer the world. Filled with negative energy, Chaos absorbed emeralds given by Eggman and after his defeat, absorbed the last emerald and became "Perfect Chaos". It was defeated by Sonic who had absorbed the positive power of the chaos emeralds, purifying Chaos and allowing it to leave peacefully with the spirit of Tikal. Chaos reappears as a bonus character in Sonic Adventure 2 and a playable character in Sonic Battle.