After what happened in Knuckles Chaotix, Metal Sonic, who last stayed in Metal Sonic Kai, was defeated by Knuckles and company, causing his pieces to be dispersed around the South Island and other islands (control of where he is geographically), Sonic and Tails. Learn to spot pieces that may be in place, thereby researching what they are, and therefore stand in line to study them, but Eggman is on his new plan to collect those pieces before they lead to old or beta areas.