The Tree of Harmony is feeling a grave evil coming to the land of Equestria it and it needs bearers for the Elements of Harmony. The old bearers were cases purely out of convenience, they were close and they were what was needed to bring about the Princess of Friendship. Dusk Shine is chosen by the Tree of Harmony to weld the Elements of Harmony and go recruit those who most truly represent the elements, no matter how eccentric they may be.
It's unfortunate that Dusk hates everypony and everything.
CAUTION!
Very strong language ahead.