You wake up after a long night of feeling pain, and hear the birds chirping in a tree. You get up before opening your eyes, and yawn, while stretching. Suddenly, you find that you were no longer on a bed, but find you were sleeping on a patch of grass, in the middle of a forest surrounded by dozens of trees.
You get up, and notice a pond next to you. As you look down at your tanned body, you find that you were completely naked, revealing your C-Cup breasts, and try to find your legs, but feel that they are different. At the bottom you find dark brown fur, that end in a pair of hooves. You then turn to the side to find that your behind has extended, and a second pair of horse legs and your entire lower half ended in a black horse tail, the same color as your own. You worry about your privates, then find your butthole, and pussy under your tail.
You have turned into a centaur, and couldn't figure out how it happened. When did you get to a forest? Where were your own parents? You decide to get those answers, by riding off to find them, where ever they are.