The Grimm Reaper, contrary to popular believe, is actually a good guy. Now you might say, "How can the reason people die be good!?" Have you ever thought about what would happen if everybody could live forever? Resources, food, water, it would all run out if the world became overpopulated. And to make sure that never happens, Grimm created 'White Rabbit'. An organization made to help Grimm save the world from it's inhabitants. Bank robbery, grand theft, homocide and genocide, White Rabbit takes care of it all.
Each of Grimm's warriors are hand picked and each and every one of them leaves those pathetic Elements of Harmony in the dust. Celestia isn't as powerful as you think.
Three years ago Grimm's number five strongest warrior left the safety of Nidhogg Island, where White Rabbit's HQ is set up, to look for any things that shouldn't be. His name.
Is Overkill.

This takes place five years after EQG. Season four never happened in this universe, thus will not acknowledge ANYTHING from that season, not Tirek, not the Tree of Harmony, nothing. There are more reasons for the crossover tag to be there then Overkill's forms being from Battlenations, I'll leave it at that. I'm sorry if the first four chapters are a bit very bumpy, it took me a long time to settle on the version of Overkill's personality he has in The Week of a Lifetime and onwards. And PLEASE, if you spot any problems whatsoever, be it plot inconsistensies or grammar isseus, ANYTHING, tell me.
Oh, and here, have Overkill's theme song!

Monster, by Skillet