When Cerberus left his post at the gates of Tartarus, Tirek wasn't the only ancient enemy of Celestia and Luna to escape. Of the many monsters that poured out, among them was the first foe that Celestia and Luna ever fought as newly-crowned princesses.

Now free from his constraints and with a thirst for vengeance against the 'false goddesses', the Frumentarii Cassius is once more released upon Equestria to sow havoc in the name of Mars. He will have his revenge, even if that means a new legion will have to be forged.

A Legion in the skies. The Storm Legion.

While the 2nd Battle of Hoover Dam may feel like a conclusion to the story of New Vegas. For the Courier who fought at it and won it for Mr. House, it was merely another chapter in his already bloody story. Now armed with a prototype long ranged Transportalponder from Big MT, Houston finds himself in a world much different from his own.

One where you don't have to kill, lie and manipulate others to get by every day.
One where "friendship" is not a contract, but a given.
One where he is the Teacher to a world unscarred by the concept of war.

A world of...multi-colored Ponies?

Heavily inspired by the works of Rated Ponystar, ShoddyCast and numerous other MLP X Fallout stories.
Note that Courier Six's backstory derives from the Fallout New California mod.