"Are you ready?" Optimus asked, trailing the ends of the silk rope Prowl preferred over the black and gold mech's plating. When the older mech nodded, he smiled. "Good. You remember the signal if you need to stop?"
"Yes, Optimus. Four two second flickers of my optics if I need to stop." The ninja shifted from his position on the floor and glanced longingly at the prime's extended spike. "May I open my panel?"
"One thing at a time, Prowl." Optimus' smile shifted into a smirk. "Hands behind your back."
Prowl obeyed, leaving his interface panel closed and placing his hands against his lower back. Optimus responded by stepping behind his partner and wrapping the silk cord around the ninja's wrists, binding his hands together and preventing him from touching himself anywhere but the small points of contact his hands made against his back and aft.
The black and gold mech sighed as Optimus' hands left his and the younger mech walked back around in front of him. "Open your mouth, Prowl."
Without even a trace of the nervous flutter that might have greeted the command a few months ago, the ninja opened his mouth. The prime removed a soft silicone ball gag from his subspace. He held it up to Prowl's face, giving himself a moment to be impressed--again--at how well the artisan he had commissioned it from had matched the colors to the ninja's preferred black and gold. Then he nudged the ball between Prowl's lips and fastened the strap behind the older mech's head.
"All right?" The red and blue mech asked. Prowl flickered his optics a single time in their pre-arranged signal for yes. Optimus smiled and traced his partner's lower lip with his thumb in reward. The older mech's comm unit wasn't disabled, but now that the gag was on, he wasn't supposed to speak. "Good. Open your chest plates for me."
The black and gold mech flickered his optics once and a moment later the mechanisms that retracted his chest plates hummed to life. The plating retracted smoothly, revealing Prowl's softly glowing spark. Optimus dragged a single fingertip across the protective crystal surrounding the older mech's spark, drawing a shiver out of the ninja.
"This too," he commanded softly.
With another shiver, Prowl retracted the crystal sheet covering his spark.
"Much better." Optimus traced the edges of the black and gold mech's spark chamber, rewarding the older mech's good behavior as well as dragging another of those pleasured shudders out of his partner. Then he pulled a tiny, lightweight spreader from his subspace and placed it between the edge of Prowl's spark chamber and the slot the crystal retracted into, keeping the spark exposed to Optimus' attentions. Then the prime drew a second, larger but equally lightweight spreader from his subspace and placed it so that it would hold Prowl's chest plates open.
Then he took a step back to inspect his work. His engine revved as he took in the sight of Prowl bound, gagged and spread open at his most intimate point--vulnerable to anything Optimus wanted to do, and trusting that there would be nothing painful. "You're beautiful like this, Prowl."
Prowl flickered his optics once, acknowledging compliment.
Optimus smiled at his partner. "Now, up on your knees."
The ninja flickered his optics again, then slowly pushed himself up onto his knees.
"Very nice," The prime's smile turned heated. "You may open your panel now."
Prowl sighed and retracted the panel covering his interface array. Almost immediately, lubricant ran from his valve and down his thighs as his spike pressurized.
The red and blue mech crossed the single step's distance between them again and reached out to touch the older mech. Prowl's groan was muffled by the gag as Optimus dragged his fingers up the ninja's spike from base to tip. "One last thing, Prowl."
The prime didn't give the black and gold mech a chance to reply before crouching down in front of him. Careful not to topple the bound mech, he rested his right hand on the ninja's left hip. Then he used his left to pull one last small device from his subspace.
Prowl vented sharply as the prime teased the clip along the rim of his valve before fastening it in place over a posterior sensor node--creating a constant, stimulating pressure as it prevented the other mech's interfacing panel from sliding closed.
"Perfect." The prime gave his partner's spike a teasing lick before standing back up and stepping away. With a wicked grin, he took his own spike in hands and stroked it firmly. "Now, don't move until I've overloaded."