You decide this is too much of a unique opportunity to pass up, besides, according to your groin you really want this, you decide the best way to approach is to do so as naturally as it would be to her. You get down onto all fours and make your way over to the waiting bear.
Suddenly, you take an inhale, a weird, intoxicating aroma fills your head, you feel it cloud your mind but you don't care, you realize your smelling her, you become overcome with lust and stick your face in her wet and waiting crevasse. Your whole body shivers as your face becomes covered in juices, you then begin to lick, not really thinking about what you're doing anymore, just letting things go, "naturally." You hear the bear growl in pleasure, enjoying her free licking. You try to do the best you can to satisfy the bear, but you wish you had a bigger tongue, more like her kind.
All of a sudden, as if triggered by your thoughts you feel something stirring in your face. First, you feel your tongue get much wider, gaining more girth, it's flatter but it's also becoming longer, you hear the bear growl even louder, she, likes what she's feeling. Now your nose feels odd, you push it deeper in, hoping to egg on a change, you are rewarded when you feel a rough texture take over your nose, suddenly the rest of your face is catching up to join it. You teeth begin to become sharper, more suited for fish and berries than the Hungry Man you had for dinner. You push deeper yet into her as your face pushes out, you feel all the hairs on your face tingle as they lengthen and are joined by new ones.
You barely even heed the changes as much as you just use them. You shove in as far as you can, using your new tongue and all of it's advantages. You don't even notice the tingle of the fur enveloping the rest of your head, or the way your ears have rounded and are on their way to the top of your head.
Very soon the fur reaches your neck and with a flash the tingling is everywhere, you decide that you need your clothes off, now. You stop your furious licking and start taking off your pants, you see your mate look at you with what could only be described as a bear pout. You sit back on your ass so you can start to take off your clothes. As you pull down your pants you begin to feel warm inside, every part of you is tingling with a euphoric feeling. Your legs begin to shrink a little, but they gain a lot of girth and fur. You quickly get your underwear off and go for your shirt, you don't notice your bear friend move near your feet.
The feel of her wet tongue over your feet makes you gasp, it slightly tickles but it sends a reaction of a different kind to your brain. You take off your shirt to see her licking your feet, well sort of feet anyway, you can't see it but you feel the rough pads forming, standing out in contrast to her smooth wet tongue. She then proceeds to take one of your whole feet in her mouth and suck it, the feeling makes you growl in pleasure but you don't notice, you're too busy feeling the fur, and the claws forming, now she does the same to the other foot. You admire your new paw, still wet with slobber. You reach and touch it with your hand, it feels so... natural, like it's always been this way. Touching the paw has made your hand begin to change as well, you see your fingers shrink and you feel your ability to move them going away, after a couple seconds it almost feels like a sort of furred club at the end of your arm. Before it's even finished forming you start to touch your own crotch, you can't help it, after a few seconds your hand paw is covered in pre, you immediately take it to your muzzle and begin to lick again, caught up in the sheer pleasure, you feel with your new tongue the pads and claws form, completing the paw. With your other hand you continue to touch yourself, feeling the roughness of the pads on your area. You also feel your fingernails grow hard and sharp, you have to be careful not to hurt yourself.
After about a minute of this you notice and absence you break out of you daze to see the bear sitting, waiting to be paid attention to again. You quickly try to stand up, you feel bad for neglecting her, but you haven't taken into account your proportions and you fall the moment you get up. You use your newly crafted paws to catch you, you land in a quadrupedal stance, feeling you hips shift to allow for two, and four-legged movement, your arms quickly gain the needed muscle to support your form as you go over to her.
As you walk you quickly notice that your entirely furred now, a thick coat of brown hair has made clothes redundant, not to mention it just feels great, you notice you smell everything now, not just her, you even smell yourself, taking in the scents of the forest will be kept for later though, as you've now made it back to your lover.
She proceeds to present yourself to you again, but this time you know things are different, you slowly get closer to her and feel your member get ready, you mount your mate and begin thrusting, using your new muscles to support you and to satisfy her. You both growl with pleasure as you increase your speed, you go deeper, deeper and deeper as you feel you member change. Suddenly you're both about to climax, you close you eyes and let go. You go into a euphoric state, you feel the change lock itself in, you know you're a bear now, but you don't care, you have a mate, and quite possibly a family on the way.
After you detach you lie in the grass with her, your muzzle resting on her back. Suddenly she gets up and looks at you, you can now tell what she's about to do, she walks away and you follow her, you follow her back to the cave where you're likely to spend the rest of your life.