Ty's colossal dick twitched, the idea of knocking up his tiny 'little' brother too arousing to ignore. Dustin was looking up at him adoringly, his free will twisted into an extension of Ty's. He was still himself, just with an overwhelming need to please Ty.
Ty placed his hands on Dustin's huge belly, letting his power seep inside--he sensed the way Dustin's intestines struggled to contain the gallons of semen, his tiny boy body aching from having a cock as big as his arm up inside him. Smirking, Ty began to change him to fit his new body's needs.
Dustin moaned as his insides stretched, his asshole twitching as he was suddenly hit with an overwhelming emptiness, which he would later learn was his ass aching for Ty's cock. His organs shifted, and from where there'd been nothing a healthy womb grew, filled to the brim with the semen from Ty's huge balls and ready to hold his child.
Ty grunted, his cock growing hard again, filled with an aching need to see his tiny brother fat with his baby. He pulled out the plug and his cum gushed out in a flood, staining the bedsheets and making a puddle on the floor. Ty ignored it, however, as he changed himself again, deciding that he wanted to breed Dustin with only the best seed.
His shoulders widened and he grew taller, easily bypassing six feet, his torso becoming perfectly v-shaped. His muscles bulged outward, his body shifting to fit his near-bodybuilder status. He felt his face reshaping slightly--he didn't want to change how he looked, he rather liked his appearance, but he made it firmer, more masculine and adult. And finally he let his thin treasure trail expand, thick blond hair appearing across his new six-pack and pecs, surrounding his huge cock and balls and across his face in thick stubble, making him feel like Hercules.
Dustin stared up at him adoringly, and Ty reveled in the size difference. He wished for a mirror on the wall beside them so he could see, and it was glorious; a massive hunk of a man, hairy, with a cock bigger than should be possible, ready to mount a boy barely as tall as his waist.
Ty decided to admire himself later, as Dustin spread his legs, his hole winking invitingly. Ty wasted no time--he pressed the fist-sized cock head to the boy's little bud, and forced it in.
Dustin screamed in ecstasy, his desire for Ty's cock overwhelming any pain. His ass was perfectly hot and tight, perfect for Ty's cock. He groaned as he saw Dustin's flat abdomen bulge, Ty's cock almost too big for him to handle, and he wasted no time in pulling out and thrusting back in.
His new muscles gave him intense stamina, allowing him to piston in and out of Dustin so fast his cock was a blur, fat balls slapping the boy's butt cheeks. Ty watched himself in the mirror, loving how his cock actually lifted Dustin off the bed--the boy had tried to wrap his arms around Ty but they weren't big enough, and was now grabbing onto the thick chest hair with one hand in an attempt to keep atop (or underneath) the bucking bull that was Ty's cock.
Feeling his climax near, Ty lifted Dustin clear off the bed and stood, using his newfound strength to slam the boy up and down, reaching even deeper. Dustin's little cock was hard as a diamond, pressed against Ty's rock-hard abs, but he couldn't reach completion since he was too young. Finally Dustin threw his head back and, in his high-pitched voice, yelled "Breed me Ty!" At that Ty lost it and came, a torrent of seed gushing forth into Dustin. Ty's cock was too big for it to escape so it simply filled the boy's rectum, a large quantity filling his newfound womb, where it would make Ty a baby.
Ty grunted as he pulled out, sweaty and tired, but having just experienced one of the best orgasms of his life. He willed his seed to stay in Dustin as he grabbed the plug from earlier, growing it even bigger--Dustin's hole was stretched and wrecked, and could've easily taken a fist.
Ty grinned as he ran a hand over his new body, eyeing himself appreciatively in the mirror. This was a good body--this was the body of the most powerful boy--MAN, in the world.
Eyes gleaming, Ty thought of what he should do next, as Dustin lay wrecked on the bed...