"...your cock," Jeff finishes. Had Mike still been rational, he would have been horrified at his son's suggestion. But if it meant he'd get a transformation, he would do anything for Jeff. His long, prehensile tail curled around to tease his shaft out of its sheath, bringing it to full hardness at an impressive 1cm.
Jeff looked at it in disappointment. "I suppose that's large for a rat, isn't it? But it's a little underwhelming... let's change that." He increased his penis to 5cm long and watched as Mike's tongue lolled out in delight. Still, it wasn't enough for Jeff.
"We need to give you a real monster of a cock, Dad. Here, try a 15cm one on for size." As his shaft grew longer and wider, now 3/5ths of Mike's body, the little lab rat laid his body over the shaft as much as he could, doing everything he could to increase his pleasure. Jeff was rather impressed. His dad's dick was now an average size for a human and looked a little out of place on the tiny rat's body. Still, he wanted to keep going. He'd already been dwarfed by his dad in strength, why not give him a dick that would dwarf his as well?
He tripled the size again, bringing Mike's rock-hard fuckstick to a whopping 45cm, or 17 inches long. Almost twice the size of Mike's whole body. All the tiny rat could think about was lust and pleasure, writhing on the floor to scrape the hot, throbbing rod over the cool rough tiles.
Jeff unbuttoned his pants, letting his own, sizable 8-inch boner free. It wasn't even half the size of his dad's, as he rubbed the two together, feeling his cock dominated by the absolute monster the rat sported. Jeff spared a hand and began rubbing Mike's dick. He only felt a flush of delightful humiliation as he realised he couldn't even fit his hand around its girth, which was as thick as his ankle. As his left hand was busy jerking his father off, he used his right to give Mike a few more upgrades.
The first thing was to increase the size of his balls until two softballs dragged across the ground behind him, and gave them no refractory period at all. Then, he made his penis prehensile, just like his tail, and his cum addictive with some transformative properties. He finally made all his father's genitalia retractable at will, as to not hinder Mike's movement.
Suddenly, a paw came across, grabbing onto his finger. With Mike's strength, Jeff could only watch as his hand hovered above a certain button, and then mashed it down.
Mike squeaked in delight as he orgasmed, blowing his monumental load all over Jeff as the transformation began. From beside his penis, a new lump was forming, growing longer with every second until it matched his first penis in size. Now with two rock-hard dicks, his ballsack expanded as four impressive testicles took up residence in it. Jeff allowed his father speech again. He wanted to hear this.
"Oh, fuck yes!" Mike yelled as his twin rods spat out gallons of precum. His voice was a lot deeper than Jeff remembered, probably due to the extra testosterone his balls were giving him. He sneered down at Jeff's prick, which was straining at the erotic sight of his lab rat dad. "Look at you. Pathetic. Your penis can't even stand up to a rat!"
Mike used his prehensile dicks to coil around Jeff's, trapping him in a super-strong cage of hot rat cock. "Face it, Jeff, I'm better than you in every way." His throbbing cocks brought Jeff to orgasm in seconds and milked his shaft dry of all of its cum. He let his son go, watching the tiny, limp prick fall back against Jeff's thigh. "Can't even keep up after a single, tiny orgasm."
With a single shove, Jeff was thrown backwards, forced to watch as Mike grabbed the 10kg plate, remoulding it with just the strength of his cocks into the perfect, metal, twin onahole. He began to thrust hard into the thick iron, fucking it without mercy. "See this, Jeff? This is what true power looks like," he grunted. "I'm super strong, hung like a horse, and I-" - he thrust hard, beginning to dent the other side of the plate - "-can't-" the dent deepened - "-be-" - the metal groaned and complained at the rat's assault - "-dominated!"
With a gasp, he tore straight through the steel, letting his thick, white sperm flood the room as he orgasmed with both dicks simultaneously. He threw the plate against the wall, panting hard. His cocks retracted back into his body, followed soon by his four testicles. The rat slowly approached his son. "So listen to me, Jeff. Every transformation you do, every second of your weak, pathetic life, every thought that crosses your mind, it's going to be about furthering me. You are going to make a perfect being, the most powerful and dominant creature in all the world, am I understood?"
Jeff wordlessly nodded.
"Good, now, I think it's time you retire for the night. You've got a big day ahead of you tomorrow, full of transformations just for me." He kissed Jeff on the cheek. "Sleep tight, Jeff, dream of my ascendency."
With that, Mike turned tail and scurried upstairs.