You are a little short for the mating, but rise up on tiptoes and manage to find her slick opening with your not-quite manhood. It is developed enough to feel amazing and strange at the same time. You push in and shudder as the doe tightens around you. The sexual pleasures are very intense, and you gasp as you thrust deep. The doe flags her tail and grunts, and you lean over her and grab her sides, mounting her more like a buck than a human.
It takes longer than you expect, your hard rod filling your mind with intense sensations, and your testicles swollen and throbbing. A low moan works out of your throat, followed by a grunt. Release comes suddenly and with tremendous force, and you grip the doe's sides as you jet far more than you thought possible from your tween's balls. When your climax is done, you collapse over the doe's back. Both you and the doe are panting, and your legs are weak as you slide out. The doe takes a few more steps, then turns and moves to lick your crotch.
You sway, but are steadied by the hands of a woman who has come forward from the group. She leans close and whispers to you "You are one with nature, one with the deer. The more you join with nature, the more you will be a natural beast." Maybe she is just being figurative, but you really do feel a connection with the doe and the forest. And... your cock and balls seem slightly off. Not that you know what they looked like before, but your shaft seems longer and the head more pointed, and your foreskin thicker than you would expect from a human. Nothing else seems different. You feel comfortable and normal moving among the people and animals.