It seems oddly fitting that Sunset Shimmer would wind up serving Nightmare Moon. After all, both were at one point the one Celestia was closest to, and both betrayed her because they felt they weren’t given the respect they were due.
Nightmare Moon would need little convincing to take Sunset under her wing… And, once the scope of Sunset’s ambitions became inconvenient, would likely dispose of her just as casually.
“Yes some ponies say it’s ironic but I think it’s only natural that those ponies with sun related identites, myself included attempt to make up for the injustice committed to our azure overlady in hopes that the sin of our previous sun-based regime can be forgiven…also there are not a lot of jobs for ponies with sun Cutiemarks in Equestrias new nigthlands and those humans kept sending “I-ar-Es” agents after me for some reason and I had to bail…”
Nightmare Moon would need little convincing to take Sunset under her wing… And, once the scope of Sunset’s ambitions became inconvenient, would likely dispose of her just as casually.