A RWBY AU story told by I'm Addicted To Breathing. RWBY is owned by Rooster Teeth, but this idea and story both belong to me.
The world of RWBY is a strange place. Humans coexist with Faunus, a species similar to humans with small difference including night vision and having an animal trait. People having aura which serves as a shield that comes from their own soul. Semblances from said aura that grant the user magical abilities such as super speed and cloning yourself. Space travel being a myth as Dust-powered devices do not work outside of Remnant's atmosphere, and the Dust itself existing with the powers of ice, fire, wind, gravity, lightning, lava, earth, and steam. Huntsman powered by their strength, aura, weapons, semblance, and teammates battle the Grimm, strange creatures that exist without an aura and with the intent of killing all humans and Faunus.
The world of Remnant is already a strange place when compared to Earth... but it's much stranger than it appears. Many people don't think that Earth and Remnant are related, that one is real and one is fantasy. But the truth is, they are both related in many, many ways. Earth gave birth to Remnant, and then the citizens of Remnant forgot about their parent planet entirely with the exception of myths and stories that were classified as "Fiction".
If that's not weird enough, then I've got more to tell you: Remnant is not a planet.
Earth is the first habitable planet, and Remnant is the first habitable zeroid. Not that soothing cream product back on Earth, anything but that. To put is simply: Remnant is an artificial planet. Designed and built by man, the "planet" has much more going on than Earth does. Of course, Earth still has lots of stuff going on such as the tectonic plates and convection currents of the mantle that move those plates, but Remnant has a lot more going on inside of it.
And yet... over time, the inhabitants of Remnant forgot about the word "zeroid". They forgot about space travel when they lost that ability soon after coming to Remnant. Earth became a myth, along with everything on it.
And so, the people of Remnant lived their lives believing they were one of the few things out in wherever they were: Remnant, the sun, the stars out in the night, the occasional comet, and the meteors that struck Remnant's surface every now and then.
But one fateful day, everyone on the fake planet will remember their past, the true past. The reason as to why they are there, the answer to the question of how they got here, and most importantly...
Realizing how much danger they are in.
Because the Grimm have a much bigger story to tell than simply being "enemy of the Huntsmen, a threat to every living thing, and soulless creatures of terror".
The Grimm's past is humanity's past, the Faunus came from the humans, and everyone on the zeroid will discover what lies beyond the atmosphere of Remnant...
Earth is not a myth.