Right before the royal sisters were born, the Royal family and its wizards wanted to create a team under the service of the Royal family. The wizards made the Sonitus, a team of special spy ponies. Although they lived with the Royal family and grown up among the two royal sister Celestia and Luna in Canterlot, their life wasn't that happy. By being a living secret is hard to hide from the average ponies. And as the time went on, slowly everything started to go wrong.
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You can see the later main character here.
Credit goes to StarFoxFan11 for helping, editing and correcting.