"Runt, I may regret this later, but I want to be a boy demon, your little brother. 9th grade hell, right?" I started to grin, then gasped as Runt suddenly completed the powerful thrust that had been pending my decision. If he spoke, I did not hear it. All I was aware of was a white-hot throbbing as he pounded into my ass, his furry arms holding me tight against his jutting chest. I was arched back, crying out as he drew out and then slammed back in like a goat pile driver. Instead of relief from the searing pain, his organ swelled even larger, stretching me inside to where I had to be tearing open. The sensations were so intense and agonizing that it took several minutes before I noticed my reflection was changing. The pain and pressure of his impossibly-swelling cock was still there, but I guess I was getting used to it, if such a thing was possible.
Runt's changes to me had already smoothed my skin and removed body and facial hair, giving me a more youthful appearance. However, there was no doubt that the young man being brutally sodomized by the goat-demon was no longer in his 20s. Seventeen, maybe. The discovery distracted me from the pain, and I forced myself to focus on our reflection. I was rising up more with each thrust, and I realized that my age was also dropping in time to his pounding. Maybe a month at a time. A dozen or so powerful thrusts and I was sixteen, my toes still touching the floor. A dozen more and I was fifteen, held aloft by his massive cock. The thrusts got faster and I could hear the goat demon grunting, bleating in pleasure as it neared climax. Fourteen was fast approaching, and Runt's vise-like grip nearly crushed me. I was crying, screaming, my nose running, pissing myself, terrified that I would die. And then Runt slammed up hard and exploded with a tremendous gush that seemed to fill my gut. He was arched back with me stretched backwards over his chest, his cock and my insides throbbing together. We stayed like that for another minute, shuddering as he ejaculated two more times. Only then did he relax his arms, curling forward to set me on trembling legs and pull that still-hot, still hard goat cock out of me.
I felt certain I was going to collapse, that I had to have blood pouring from my torn anus and ruptured colon. But the only thing dripping from me was sweat. A soft hand gripped my shoulder and I looked back in the mirror to see the beautiful man-boy Runt smiling at me over my shoulder. But this time he did not have to stand on tiptoe. He towered over me by a head. Pain and heat were fading quickly, and as strength returned I began to examine the boy standing in front of Runt.
He was stunningly handsome, the kind of kid you see in movies or television shows as the 'good' kid, or modeling expensive clothes in magazines. The reddish-brown hair and bright blue eyes remained, but I did not recognize the features at all. This young Adonis was a stranger to me. Well, I did recognize the sexual equipment, which had not shrunk in proportion to my body. That would make pants a little tight. An odd sensation pulled just over my butt, and a long barbed tail the same golden tan as my body twisted up from behind me. With a thought, I was able to wrap I around my belly, then drop it down between my legs, and arch it up between them under my enormous testicles. Runt's hand rubbed the base and I shivered at the pleasurable touch. Oh, yes. it was sensitive.
He reached around with his other hand and brushed aside the thick hair hanging over my forehead to reveal the polished white protrusion of a horn just ahead of my right temple, and repeated the action to show me its twin on the left. I drew in a shaky breath, staring at myself and then him in the glass, then turned to face him. He draped his arms loosely around my back and grinned. "Hello there, little brother."
I stared up into his eyes, mouth still hanging open in dazed shock and amazement. He leaned down and kissed me, flicking his tongue across mine, and then drew back. That was enough to jump-start my brain again, and I managed to croak out "Ouch."
Runt laughed, then embraced me hard again. "Ouch, indeed! I thought I was gonna come out of your mouth!" Then he pulled back with a grin. "Only done that once before with a guy who wanted to be my cock. If that didn't make him happy, I don't know what else would."
I blinked and stared down at his now-flaccid, if huge, human cock. "That used to be a person?" He nodded and hefted the meaty shaft. "Jack Powell, a thirty-something stock clerk I met in 1937. Don't worry. I believe he has developed quite a taste for piss and cum."
Runt looked me over. "Let's talk about you. Maybe a little far back for 9th grade. But probably eighth and seventh for sure. Happy with the results?"
I looked down at myself and then twisted around to stare in the mirror. My face was streaked with sweat, snot, and tears, but it still belonged to the most beautiful boy I had ever seen. "How come I'm not a goat-demon?"
Runt shrugged. "You wanted to be a demon boy. Back in the 1700s, when I got turned, demons had a certain look that was expected. I still use it for some folks, but most prefer this shape or a variation."
I blinked. "You're a couple of hundred years old?"
"287 to be exact. Next month." He grinned. "Better alert he fire department if you put candles on the cake."
"So, will I grow up to look like you do now?" There were enough similarities in our faces that I could easily be a younger version of him."
"Not gonna happen." Runt chuckled. "Growing up, I mean. If you grew up you wouldn't be a boy demon any more. This is it. Your true form forever. At least in this world."
It took a minute for me to process that. I was immortal. A demon Peter Pan. "But, what if I want to do other stuff. Like be a minotaur, or a goat demon? Or just an older or younger kid?"
Runt tousled my hair. "It will come! You have to learn to use the powers you have. But it won't take long. Between me teaching you and you playing with your schoolmates, you'll have transformation down in no time."
I had a hundred more questions, but a wave of fatigue slammed into me and just about dropped me to my knees. "Oops! Time for sleep." Runt scooped me up easily in his arms and carried me over to the bed. "This will probably be the last time you really need sleep, but the initial transformation always takes a lot out of you. Well, actually, I took a lot out of you to transform you." he smiled at my questioning look. "I'll explain when you wake up. Don't worry. I'll be here."
There was no fighting sleep - my whole body shut down so suddenly that I was unconscious the moment my head hit the pillow.