The story is set in an alternate universe where Luna doesn't become Nightmare moon. Instead, Celestia is the one that is jealous and she turns into Day Breaker. Luna easily defeats her and the prophecy of Day breakers return is still the same but this time, she was banished to the sun and doesn't burn since she is the essence of fire. The events afterwards plays the same except that Cadance and Shining armor had Flurry Heart early and Queen chrysalis was defeated by Cadance very easily, Luna becomes Twilights teacher and master, Zecora was well respected instead of being feared from the start, Flurry heart mastered her powers, and Starlight Glimmer got her Cutie Mark alongside with Sunburst.
Day Breaker wasn't defeated by the elements and turned back into Celestia, she retreated and started to plot. She orchestrated a disaster that took away spike's life and unhinged Twilight to insanity. Daybreaker takes advantage of this to use her as her pawn. Zecora forms a resistance to stop Day Breaker and Twilight. Will they win?
Note: Give me time, I might not be committed to finish this since I have school
Sounds like an interesting plot and I look forward to reading it. However I think it might be beneficial to trim up your description a bit. It kind of comes off like a lot of information just being dumped on the reader, these seem like things that should be learned as we read.
10769448
Agreed.
Don’t be evil, Twilight!!!!
Be a good nice Pony like Cozy Glow!!! 
Twilight is a Dumbass Idiot!!!!!!! I DON'T care that she is consumed by Grief or even "Insanity"! Why join the very same person ( Day Breaker) that TOOK Spike's Innocent Life in the first place???!!!
I DON'T care if she will reformed back to normal or not. She should be Punished for her Actions, and SHOULDN'T be Forgiven by the Pony Populace for a long time.
By the way? What happened to the other Mane Five?! Could they might help and reform Twilight?
She didn't know that it was day breaker. I'll explain in the next chapter
10770110
this will b explained later in chapter 3.... Whenever I make it
10770438
Ok. But what do you think on my first comment on NOT liking Twilight's decision?
10770442
She was loosing her mind. She couldn't think straight after seeing her "son like" figure dead. She didn't know that it was Day Breaker that killed spike. Day Breaker manipulated or charmed her into promising that She would bring spike back. Think of it like Darkseid but no anti-life equation.
10770452
Even without the Anti-Life Equation. Darkseid is still OP and a Scary DC Comics Villain/Tyrant!!!!!
10770463
Yesss hahaahah
I have a question. Will Spike appear in the fick later, or does he just want to be killed? (Just judging by the description of the fick)
10771053
I hope that he could be resurrected. Just so he could KNOCK SOME SENSE to Twilight.
10771053
Yeah spike will appear later..... And he will be killed
Please refrain from putting unnecessary sentences or other stuff like that into your story, it breaks immersion and the flow of the story. Which is something you should never do. Because it come off as bit amateurish.
If you're not sure about a certain term then please look it up on google or something during the writing and editing phase prior to submitting the chapter.
There also another stuff you could improve in terms of writing a story that other commenters have already mentioned. If you follow these constructive criticism to heart and surely you'll be a good writer over time.