The CMC always want to be like their big sisters or in one of their case sister figure. As in being heroes who will save the day. Now opportunities present themselves once their join the kid next door and save children from adult tyranny.
When Discord stole the Elements of Harmony, Luna summoned the greatest warriors in the multiverse, Sector V. Only 2 problems, 1 they're now ponies, 2 Luna has no idea how to send them back.
The CMC find themselves in a world much like their own. Except that here, blank flanks, who have taken on a very familiar name, fight for what's right against the tyranny of those with Cutie Marks.