Based on the video game and cartoon, Afro Samurai:

She watched her sister be murdered before her very eyes due to a legendary jewel that she possessed, based on a fable.

With her only family gone, Sweetie Belle travels to avenge Rarity with nothing but a scythe given to her by her former fillyfriend, Apple Bloom with Scootaloo joining her, through no will of her own….all while searching for the mare who took everything from her….Twilight Sparkle and her assistant, Spike the dragon. Why her sins follow her dark path with every hoofstep.

Very slight pairings of Sweetie Belle/Apple Bloom and Fluttershy/Rarity…but nothing that even goes pass the rating of Teen.

Also cerdit goes to the bad ass artist Grenaddas for allowing me to use his/her cover art.