i swear alot ZER0 is a deformed version of Sonic who was once possessed by a EXE, but for reasons unknown, the anomaly was forced out of his body, which deformed the body in the process.

Biography
One day, Sonic was running around green hill when he stumbles across a cave, one that lead to a Labyrinth Zone adjacent area. At the end of the zone, he finds a chest that is encased in diamond. As Sonic broke through the diamond and the multiple padlocks, he thought to himself, “Whoever put this here