Onyx pranced and kicked up loose metal like a bucking bronco. The deep brown and gold centaur-esque Prime was snorting and grunting with his wings flexing, wanting to twitch every so often. He was pissed and excited.

The free form of Amalgamous was taunting him. His yellow electricity and free flowing parts that hovered around their respective areas moved considerably now. A sign of blatant disregard for Onyx's rising eagerness. The two arms on his back gestured towards Onyx while his main arms were slack on his hips.

He then reverted to his condensed Cybertronian form, all the loose floating panels combining to a solid form and his electric interior was hidden from sight, only reflected by the yellow of his optics and bio lights. The extra arms on his back shifting to instead be kibble. His pronounced smile had a hint of canines to match his mischievous behavior. His rows of small horns were equally a reminder of his real form.

Onyx was waiting; Amalgamous knew the drill. Whenever Onyx wanted to frag, he would summon Amalgamous. He was one of the few Primes who could take his rough treatment, and Onyx was in a very rough mood.

Stomping his front left hoof, he sneered, "Amal, I hope you're prepared."

The shapeshifter hummed cockily, "Never."

Onyx trotted closer and revealed his spike near the farther end of his horse-like underside. Huffing, he was desperate to use it and frag Amalgamous to the ground. His needs only grew watching the faded gold and bronze mech reveal his glossy valve adorned with yellow bio lights.

Amalgamous climbed up in front of a low-rise platform near Onyx's lounge berth and had his back facing the other. Onyx came closer seeing him place his knee on the bar below the platform and hiking his other leg to rest on top of it, giving the beastly Prime an excellent view and access to the already dripping valve. Amalgamous seemed to have been anticipating this for the day. It made Onyx flash a mouthful of fangs. He enjoyed the brief show of Amalgamous reaching back and stroking his valve petals.

With a growl, he raised up on his hind legs and let his forelegs catch to straddle Amalgamous' sides. His spike swiftly entered, earning him a hiss and a momentary groan. Unlike the other Primes who had normal body structures, Onyx's centaur self was not subtle with its range of motion. He couldn't pace his hip thrusts. His thrusts were sharp, strong and went deep quickly, painful for most types of bots but Amalgamous loved it.

He purred as he gave a thrust every other few seconds, sending the spike jabbing hard into Amalgamous' inner abdomen. His lover grunted and snarled in a pleasurable way, jolting each time the spike snapped forward. His opening could take it.

Onyx gripped the pillars between their space with his heavy claws, panting as he managed to make the thrusts now once every other second. Tight, so damn tight. He closed his optics and focused on the body below him gripping the platform.

"F-Frag, umph! Mmph!" Amalgamous cried, "Yes!"

The harsh thrusts were snapping into Amalgamous like a whip. The beastformer only had so much he could take. His stamina was slightly different; he aimed only to overload himself. Amalgamous tried to meet against the rut regardless of this knowledge. Onyx felt heavy and drowning in bliss until the dam broke.

Suddenly, a horse-like roar echoed as Onyx overloaded and staggered back, letting go and slipping out of the other mech. He had so much transfluid, it filled Amalgamous and spilled out on the ground for a good couple of seconds upon being free of the constrictive heat. His body didn't like to hold back and felt like an asshole leaving his lover gaping and unfinished, but Amalgamous didn't seem to mind the quick overload because he went right to work finishing himself off.

Onyx stared among his cooldown at Amalgamous fingering his pretty valve. Onyx's transfluid was getting everywhere the faster he pumped. It made the beastformer horny again. Amalgamous' form threatened to dismantle as he clawed the platform he was laying his chest on, valve solely for Onyx's sight only.

Heavy sounds and leaning up to arch gave Onyx a splendid view of his lover's orgasm. Amalgamous took out his digits briefly with a gasp, letting the transfluid and his lubricant spill out before returning them to rub at his valve to stimulate another quick rush then succumbing to his body's needs. Onyx's animal intincts were kicking up with the urge to take him again.

Amalgamous finally looked at Onyx with his yellow optics pulsing, "I love it when you're like this, but I don't think I'm full yet."

The centaur purred as Amalgamous climbed down to sit on his calves, letting the transfluid leak out tauntingly slow. He then went on all fours and shifted parts of his back to give himself a reptile-like tail, wagging it alongside his aft to show off. It was enough for Onyx to immediately prance and stand over him, placing his servos on the pillar in front of them as Amalgamous grabbed his spike. It was brought to the gaping valve full of cum.

Onyx grunted as his spike was forced into his lover but let Onyx wiggle it as deep as he wanted and pumped it in and out of him at his own pace. The beastformer wanted so bad to kneel on his front legs and pin him to thrust hard, but it was only fair to let Amalgamous take charge a few times too.

One thing was for certain, he was going to fill every part of him with as much transfluid as possible before they were done.

AN: We doing this, every pairing you can do with fifteen Primes total. Keep in mind Thirteen and Optimus are going to be the same character in this and the personality will be based more on Thirteen. The other two extra Primes will be Zeta and Sentinel. In some universes (Aligned...cough cough), they are the same character...weirdly. The character is Sentinel Zeta Prime and he goes by both names. We aren't doing that, Sentinel and Zeta will be separate. Look forward to updates every other day!