Long ago, Duchess Starlight Glimmer used her magic to take away the cutiemarks of many ponies to make her own world of equality. Using the power of the cutiemarks, she fueled her own form of Lust.
In her world, lived a stallion named Sunburst. He was her childhood friend who had to leave her in order to pursue his magic studies cased by his cutiemark.
In a castle not far away, lived a mare named Twilight Sparkle. Due to the loss of her friend, Sunburst, she visited Starlight and ended her and her Lust.