you were sitting in your high school, in a class like any normal person. Eventually the teacher came in, holding a strange syringe and your classmates started muttering amongst themselves.

Teacher: uh, well a group of scientists wanted to test a new medicine… we need a volunteer for it…

your classmates started muttering amongst themselves again, but before any of them could, you chose to volunteer and went up front. As soon as it was injected, you began transforming into an anthro animal or creature. Everyone was surprised by this.