Once upon a time, in the magical land of Equestria, there were two regal sisters who ruled together and created harmony for all the land. To do this, the youngest used her unicorn powers to raise the sun at dawn; the older brought out the moon to begin the night. Thus, the two sisters maintained balance for their land and their subjects, all the different types of ponies. But as time went on, the younger sister became envious. The ponies only labored in the sun that she brought forth, but gazed at the stars and played through the night. One fateful day, the younger sister refused to lower the sun to make way for the night. The elder sister tried to reason with her, but the bitterness and envy in the young one’s heart had transformed her into a wrathful mare of ceaseless fire: Solar Flare.
She vowed that she would shroud the land in an eternal day, scorching the land. Reluctantly, the elder sister harnessed the strongest magic known to ponydom: the Elements of Harmony. Using the magic of the Elements of Harmony, she defeated her younger sister and banished her permanently in the sun. The elder sister took on responsibility for both sun and moon, and harmony has been maintained in Equestria for generations since.

Dusk Glow was just an ordinary unicorn when she was thrust into an alternate version of her world. Now, she has to be a hero.