No humans. In Equestria's past, ponies exist only to serve their creators. One such pony is accidentally released from her mental chains, but how can one mare save herself and her people if she doesn't even know she's a slave?
Princess Celestia has been keeping a dark secret from her subjects for a very long time. It's not an easy truth to tell, but if anyone can accept her after learning it, it will surely be her most faithful student.
My unicorn parents called me a worthless mud pony. They pushed me every day to overcome my lowly status. When I woke up one morning with my cutie mark, I thought they would love me. I couldn't have been farther from the truth.