There is no need to watch either MLP:FIM or RWBY. Since those stories will be revealed if they are called upon. Although it would be useful if you atleast know Ruby Rose, Twilight Sparkle. And the basic storyline of RWBY.

There are two stories. One girl is destined to be a princess, the other to be eaten by a big bad wolf. How do they correlate? Both girls are doing so, against their wishes. But both are doing it for a single reason. To help others. What if both stories intertwined in ways fate had not destined for them. What if one changes the other into a great warrior, yet the one into a great martial artist? One has magic, the other aura.

This story takes places several year before the show starts, the show known formally as RWBY. Yet as a original tale of my own. As Twilight is a filly thus a child. Finds the child version of Ruby Rose, nearly mauled by great big bad wolf. As children they shall grow, into great warriors will they bloom. Believing in the forgotten. Accepting the past as the past, the future as a mystery and the present as a gift.