One day while Sonic and friends were in the middle of a battle with Dr. Eggman, the egg-shaped scientist injected Sonic with a serum that can make anyone sick with a terrible disease that wiped out some of the hedgehogs many years ago. A certain disease called, the Blue Flu. Hearing that Sonic was sick, Rouge called someone to take care of him, and that someone was Shadow the Hedgehog himself. Shadow didn't want to take care of his rival, he'd rather kill him if he got the chance. But, he only accepted the offer for the money Rouge promised she'd give him after.