Title: The Demon Queens of Sin

Main Characters: Twilight Sparkle, Flash Sentry, Spike, The Mane Six.

Genre: Anthro, Alternate Universe, Crossover, Romance(NSFW), Adventure, Comedy.

Crossover: Seven Deadly Sins (Manga/Anime)

Pairings: Flashlight, Sparity.

Premise:
Long ago, the Kingdom of Equestria was threatened by Midnight Sparkle alongside her faithful Dragon companion and the strongest, cruelest (and most beautiful) order of her demon army: The Demon Queens of Sin, each one bearing the symbol of their Sin:

Applejack: Queen of Envy (Leviathan)
Pinkie Pie: Queen of Gluttony (Beelzebub)
Rarity: Queen of Lust (Asmodeus)
Rainbow Dash: Queen of Pride (Lucifer)
Fluttershy: Queen of Sloth (Belphegor)
Spike: King of Greed (Mammon)
Twilight Sparkle: Queen of Wrath (Satan)

However before they could overthrow the Kingdom, they were defeated by a powerful group of Ponies and were sealed away to be forgotten forever…sadly, the warriors that stopped them were killed in combat. In memory of their saviors, the Ponies founded the Celestial Knights in order to honor them. However, over the years the Celestial Knights grew corrupt with power usurped the ruler and subjugated the rest of the kingdom.

Flash Sentry, a former Celestial Knight who eventually rebelled against them and has traveled the land trying to form group that might be able to defeat them, sadly he is found and pursued by his former comrades. Upon discovered an abandoned temple, he hides out there only to find a coffin with a sword embedded in it. He’s forced to take it out as he’s cornered by the Knights… only to unintentionally free the Demon Queen of Wrath.

After she defeats the Knights Flash explains what’s happened in the last several years, Midnight, outraged that her army has been defeated and disbanded decides to go on a quest to find the six remaining Sins, taking Flash along as well(not that he has a choice). However, their quest will not be easy, as the Celestial Knights are now hunting for them, and will go to great lengths to capture or destroy them...