You know the typical TCB fare, right? Either humans or ponies are "pure evil", and the "pure good" comes out on top. However, this time it isn't so simple...
A good Celestia that replaced the original Celestia of this reality.
Ponies that somewhat question Celestia when the truth gets out.
An immortal human that judges all Celestias as monsters, and believes that none could ever be pure.
Humans that are indoctrinated to hate Celestia before they even meet her.
And a long-destroyed relationship that is trying to heal...