Fiction's Upper Limit Lore (FULL)

>>> Avoiding your common set-up.

I'd have to judge that mind-control and being raised by the enemy since birth is common to uncommon, not rare.

The details of what happens to Terra during the events of the game is up to the fans. The owners, designer's, and other memebers of the creative team have the final word on what's canon.

As you know an expedition by Gesthal retrieved Espers from behind a sealed gate. Chances are this is already public knowledge. Or at least anyone in the military would know about this and the empire's magic powers.

I'm pretty sure the world remembers the war of magi. Once Terra grows up to learn the truth she might defect from the empire being half-esper. But Terra was rescued by Tritoch and met up with Locke.