Thirteen had rode Prima's spike before, once from seducing him and another letting himself be pinned. But this time, he wanted to do something a little different. When he conveyed to Prima that he wanted to use his spike this time, he expected him to be dismissive. He was surprised to learn Prima had no qualms against it. They met after daily drama between the other Primes settled down, and he didn't hesitate to lay back on the couch as Prima commanded. As the leader, Thirteen also expected him to be in charge and it stuck.

Prima crawled over him and leaned to graze his lips against Thirteen's. "Ready for me?"

"Yessir," said Thirteen rather quickly.

His servos were suddenly pinned by Prima's and he watched the mech sit upright to align a silver mesh valve with pretty white bio lights radiate over his spike tip.

"Thirteen, just relax and let me take care of everything."

Thirteen's chest heaved as Prima sank onto him. The valve took him in completely and suffocated him with a flushed expression from his mentor. Then Prima lifted up and sank back down at a slow pace. The valve made his spike warm and slick. He watched it rise and fall on him with Prima letting go of his wrists and instead displaying himself perfectly. Thirteen looked up at his mentor in awe.

Prima twisted his hips down in an expert motion that made Thirteen buck up. His mentor leaned back with one servo on his thigh for support and the other on his abdomen. Thirteen made a brief noise when the larger mech started going down faster on him. He could only palm the mech's lower thighs while his spike was being bombarded.

"Feels good, doesn't it?" Prima panted, "It certainly is perfect for me."

The red and blue mech couldn't do much in his position and just marveled at the ferocity of Prima's determination. He bit his lip and threw his helm back as a sticky mess was starting to form between them. Each time the valve went up, he had seen strands of lubricant attached to him and the valve only to be coated with more back down. His chassis was jolting a little each thrust onto him. A range of contentment and lust rolled off him in the hard motions.

The drowning nature of his system's heat made him lay there like dead weight as his overload built up. Prima was riding him faster with his engine and vents roaring. Thirteen's vents were stuttering. The couch sounded like it was close to breaking.

Thirteen grunted and cried out clutching Prima's hips in a hard overload while the latter panted and chased his upcoming orgasm. He switched to hold Thirteen's servos down again and down at a new angle that drew out his pleasure. Thirteen never saw Prima arch and gasp upon finishing, calling out his name so forcefully. It changed Thirteen's perspective on his mentor. Processing this emotion among the cooldown, he loved Prima and the amazing interface they had.

"You were excellent," Prima said as he got off of him.

Thirteen stared at the glob of mixed fluids leaving Prima's valve and sinking onto his spike upon departure and groaned at the sight. He wasn't satisfied. He wanted Prima to be back on his spike and being fragged by him hard. He liked seeing the mech use his nice valve and ride him. Grabbing Prima's hips, he made the other mech pause and meet his determined optics.

"Please, Prima, do it again. I want...this"

Prima grinned and reached down to widen his leaking valve for Thirteen's arousal. "You like my valve so much?"

"Y-Yes, sir...please! I just need it! One more time..."

He moaned as the Prima grabbed his spike and teased his entrance again, purposefully making the tip barely press in before being left to rub against the folds. The death grip on the other's hips made Prima just laugh and quickly grab his servos to hold them steady but humped his length before finally seating himself again. This time, Thirteen tried to assist but had his servos gripped to not interfere. Prima was back in control.

It was pure heaven to him feeling his spike being beaten by the valve that consumed it. Prima rode him hard where he believed his pelvis would soon break, but it would be worth it seeing the Prime leader taking him entirely and watching his spike disappear over and over again in the addiction.

"Thirteen...oh frag yes! You don't disappoint, ah oh! Frag me! That's it!"

It was technically Thirteen being fragged hard. He still couldn't match Prima's demanding power in their interface. He was just useless and loving being used. He wouldn't even mind if Prima only used his valve for now on. All he knew in his horny mind was that Prima felt so good. The couch still sounded like it was about to give out.

AN: Prima is a slut and we all know it. He wants to get away from his job so bad, he'll take anything. Thirteen's really just kind of there enjoying his spike being fucked.