Sonic and his friends' planet is attacked by a new formidable enemy called the Metarex. Sonic struggles in the fight and scatters the seven Chaos Emeralds across the galaxy, and a lone Metarex ends up robbing the planet of its life source, the Planet Egg. Then, an 18 year old Chris warps to Sonic's planet using a machine he created, but ends up reverting to the body of a 12 year old due to a time dilation between the worlds.