I'm a Spark (That Won't Go Out)

Sonic was not always "Sonic". Once, he was Guard, the creation of the Ancients whose only purpose was to protect his people and the Chaos Emeralds from harm. When the Great Destroyer came and wiped out all life, he was left on his own, no one to talk to for thousands of years. One day, a plane lands on Kronos island, and three mobians find a tired hedgehog standing guard in front of a dilapidated temple. This, dear readers, is where our story begins.
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An AU of Sonic Frontiers where Sonic was made by the Ancients to protect them and the Chaos Emeralds / Cross posted on Ao3 under the same title and username (updates there first)