Many years ago, when a magical comet hits the Earth, all the animals that are effected by its radioactive mushroom cloud have evolved into Mobians, anthropomorphic versions of themselves they have become. Due to their evolution, this gives them hyper-intelligence and the ability of human speech. However, some of the animals remained unchanged because their projectiles made them immune and pure at heart.

Years later, the Mobians began to experience non-natural coloration, developing those with the rainbow of colors. However, some of them retained their own coloration which remained unchanged forever. As time passed, half of the Mobian race developed extra-additional body parts as well as distinguishing features, such as fairy wings and tiger stripes. These Mobians born with those are special and can experience even better than the other half of the race. Though they are still part of the ancestry.

Years after that, a cobalt-colored egg, which was cared for by Sakura, hatched into blue-furred Mobian hedgehog with two heads, each with its own mind and personality. They are named "Sora" and "Nicky" because they share a single body. Despite this, the twin brothers obtained the ability to run faster than a speed of light, naming each other a portmanteau of their own names: Sonic the Hedgehog.
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My original Sonic AU, Sonic In Two Minds!!