You pull off the tissue paper and find a leather harness, the kind you'd see on a leather bear. It looks like it's designed to be worn around the torso with a metal ring in the middle of the chest. The mysterious package also contains a shiny leather jockstrap and a studded collar. The buckles on them implied that all three items are meant to be worn together.
"I'm not leaving the house dressed in this!" you say to yourself. You'd be arrested for indecent exposure at best, and you don't want to spend a night in jail clothed like that.
It's not long before your mind turns back to your gift. "I don't have to go outside in it, but I wonder what it's like to wear it..." you muse. "What the hell. It was free and I'd hate to disappoint my admirer."
You head into your bedroom and make sure that the curtains are closed, you don't want anyone to see you dressed in your gift. You strip nude and slide the leather jock up your legs. Your admirer must think a lot of you as the pouch is over-sized. "This must be built for a porn star."
You then put the harness on your chest. Once again your mysterious benefactor overestimated, the harnesses' tightest fit still hangs off your frame. You then clasp the collar around your neck, it too is too loose.
"Can't forget to bind this together" you laugh as you snap the three pieces together. You feel a shudder as you do this. You then head toward the bathroom, wanting to see how foolish you look in the mirror. Your modest build barely holds the thing on. The harness and the jock's pouch droop. You turn to leave when you notice something odd.
You shaved this morning but now your face is sporting several days worth of stubble! You get close to the mirror for a better look and you can see the hair growing! It continues until you have a two inch long beard on your face.
You back up in disbelief, wondering what is happening. It is then you notice your chest, you're gaining more definition. Your pecs get buff and a six pack materializes out of your gut. Your arms similarly swell with muscle.
You think you can deal with this beard if it comes with being buff, but the change is not finished yet. As you strike a pose before the mirror, you notice that your definition is fading. The muscles aren't atrophying, you can still feel them. It's as if a layer of fat is covering you. Your gut becomes large and round but firm, you have to loosen the harness before it tears.
You think that your body has stabilized when you see hair beginning to spread up from your crotch and down from your beard. Growing just as rapidly as your beard, the hair covers your chest and spreads across your shoulders and down your arms, giving the backs of your hands a manly covering. Your legs are similarly girded in hair.
Gazing at your new hirsute body you notice that your leather gear now fits you perfectly... even the leather jockstrap. Totally freaked out by what just happened, you strip off the harness, take off the collar, and lower the jock. A 9-inch long tube of meat the thickness of a beer can flops out of the pouch. You notice that a foreskin has reappeared on your formerly cut head. You also notice that a hairy and pendulous ball-sack now hangs down between your legs.
You look back into the mirror at what you have become. You are now a leather bear.