Millennia ago, the Chaos and Master Emeralds were kept at an altar near the territory of a clan of echidnas (the Knuckles Tribe). A peaceful echidna named Tikal, daughter of Chief Pachacamac, befriended the Chao that lived at the altar and their protector, the water god Chaos. When Pachacamac sought to expand his clan's territory, he wanted to steal the Chaos Emeralds and use their power to defeat his rivals. Although Tikal and the Chao stood against him, he ordered his soldiers to charge anyway, resulting in many Chao being injured. This enraged Chaos, who transformed into a terrifying, giant monster and destroyed all of the echidnas, save for Tikal. Tikal sealed herself away in the Master Emerald with Chaos, and the magic caused the area surrounding the shrine to become Angel Island, the continent in the sky.
In the present day, Doctor Eggman learns of the legend surrounding Chaos. Believing it to be true, he seeks out the Master Emerald and shatters it, freeing Chaos in the process. Eggman's goal is to control Chaos, and use its destructive powers to collect the Chaos Emeralds and conquer the city and turn it into "Robotnik Land." To help him, he has created the E-Series robots. When Sonic the Hedgehog learns of Eggman's plans, he and his friends spring in to action to stop Eggman and they start another journey for the Chaos Emeralds.