You were a hybrid abandoned in a lab, left for dead. The other experiments starved and died, but you got out of your chains and got around for food. Someone found you, and tied you to a tree with a rope on your wrists and around your neck and waist, and a muzzle on. A soldier, Keegan, stumbled upon you, and knelt down, "Hello, pup/kitty.." he says with a smile.