It take place during the season 3 of sonic x. Bad ending of sonic forces all sonic friend are dead except classic sonic and Modern sonic who tries to fight infinite but they failed even his super form.Infinite got a new plan: destroy all the demession of universe.So Classic sonic return his past and Modern sonic travel to another demession to stop him. He meet up with himself and his friend in another dimession. Will they help him to stop Infinite and the metarex. Tailsmo and Sonic and Cosmo relationship is very sibling-like