Matt hmmed, "I think I have an idea, why not have the power to change each other, perhaps via a trigger". "You mean like the heat in Turboteen?", Jacob answered. "Yeah, but perhaps it could be something we could do to each other" Suddenly they both grinned and Jacob sat down on the computer, making some inputs and hitting start.
Suddenly both of them were engulfed in a strange light, seemingly dissolving all of their details, turning them and their clothing into vaguely human blobs. Gradually it got back its definition. At first you could see that Matt had bulked up quite a bit, while Jacob barely seemed to change his build. On both blue one-piece jumpsuits started to appear with red straps and black pads apparently to give some protection and buoyancy. Black boots appeared on both of them, as well as black fingerless gloves. On their heads blue helmets with a red triangle appeared which were open to reveal their faces which were paradoxically obscured by a black bandana. They both had a headset.
Matt looked at himself and then his buddy, "Fancy design, we look like superheroes. So how exactly does it work?". Jacob opened the zipper of his suit which bizarrely also opened from his ass, "Well you do me first, then we'll swap." Matt also unzipped his suit and as Jacob got on all fours he pushed his already erect member into Jacob's ass. Suddenly a wave of arousal hit both of them.
Jacob's body started to stretch in impossible, his nose stretched out to an impossible length, and his mouth and face bulged out forwards. At the same time his arms grew and flattened. His feet curled up forming black cylinders which gradually looked more and more like wheels. On his back hump started to form, segmenting into parts. Further back a set of fins started to grow upwards and to the sides. His ass-cheeks also changed and became both rounder and pointier before sagging in in their middle. Then Jacob's nose hit the wall and he realized, "Damn, I'm not going to fit in here." Matt quickly pulled out and almost fell back on his bum as he started to calm down.
In front of him there was this huge creature, part human part fighter jet. It filled a good portion of the room and while some parts already looked very much like a plane, others were distinctly human like his penis which still hadn't changed much, except for size. Jacob slowly started to revert to his human form, shrinking again with metal turning back to flesh and cloth. Matt was curious, he started to poke Jacob's member which made his buddy moan and shrink by quite a bit. Then he started to rub on it, which made Jacob moan more and change somewhat quicker to his human form. After a few minutes only a set of fins poking out a bit of his lower back remained soon to vanish.
"So it's my turn now", Matt said as he was getting down on the flor on all fours. He selected a place with some room around him, "Hope I'll fit in" Jacob measured the room estimating if Matt's form would fit, then he got down to him and pushed in his member. As Matt was much more massive Jacob could almost stand, holding himself on his back. The same wave of pleasure went through both of them, and Matt started to change.
At first his helmet grew, obscuring his head. At the same time a lump appeared on his lower back growing upwards and becoming more and more massive. His balls started to grow massively turning darker and darker as his legs folded in, resting his weight on the wheel that had grown out of his ball sack. Then his helmet also grew upwards creating a sort of wind-shield. The hump on his lower back had grown in size joining with his ass. A pair of fins grew out of it. On the rest of his back, black leather pads started to grow. His arms retreated and his hands grew into blobs which reformed into a front wheel covered on top by what used to be Matt's helmet. Eventually his feet couldn't touch the ground anymore and his member which became much longer and thinner turned into a kickstand for him to balance on. After what was a minute or so, Matt was a full futuristic motorcycle.