It was going to happen soon, he just didn't know when.
Optimus had grown used to his role as Prime - he knew the signs for when Primus would demand his penance yet again. The ground rolled slightly as he wandered through the streets of the newly restored planet; a low rumbling and small localized tremors occasionally happened.
His memory told him that he would have at another day; he was wrong.
And so, when Primus came for him, Optimus was bound, faceplates down, to his own berth, arms and legs spread wide, vocalizer and optics forcefully offlined. Standing over him, Ratchet and Megatron worked in tandem. The medic skillfully teased the Prime's valve, one servo exploring the inner cavity, dancing over the inner nodes, while the other lightly flicked out a rhythm over Optimus' anterior node. Megatron held an electro whip, bringing it down with practiced grace - each stroke hitting yet another untouched part of Optimus' back and making his entire frame stiffen from the combination of the pleasure and pain.
Megatron finished his count. "Impressive, Prime," he said, setting the whip down and running a claw down Optimus' tender back. "You have endured, suffered, and now, you're ready for me to make you mine." Optimus exvented, shivering with desire.
"Doctor, I trust he's good and ready?"
Ratchet just gave Megatron a wicked smile and -
An earthquake rumbled through the building, snapping everyone out of the scene as the building shook - a collection of toys on a nearby dresser fell to the floor from the vibrations.
Ratchet sent the command to free Optimus from his restraints, and found that Optimus had already sent the safe-word himself, and had closed his valve cover. His face flashed worry for a moment, before settling back into the stoic expression that Optimus hadn't worn since the treaty.
"I must go - you may follow, but I cannot guarantee your safety."
"Oh, no you don't," Ratchet and Megatron said simultaneously, both reaching out and grabbing a shoulder each.
"This is my duty as Prime," Optimus said, not looking back, "This is… I can promise you my own safety, but I cannot promise the same for you."
Ratchet rolled his optics at Megatron, "And we're going to follow you anyway," the medic said.
"Very well." Optimus stepped outside just as a second earthquake began rumbling. Megatron and Ratchet followed - Ratchet's optics scouring everything, and Megatron's fusion cannon charged and held at the ready.
Optimus, once outside, knelt down, knees spread, in a position that his trinemates recognized immediately. Without warning, the groundmetal cracked and rolled up around itself in more places than either of them could track, forming tendrils that wormed their way towards Optimus. The first two to reach him wound up his arms, squeezing them tight. Immediately, another pair wound along Optimus' legs, and the four tentacles lifted him bodily into the air.
Megatron's blade slide out from under his cannon. "OPTIMUS!" he roared, about ready to charge.
"MEGATRON!" Optimus shouted back. "Stand down - unless you want Primus to attack for interrupting the creation of newsparks." Smaller tentacles had begun winding across his body in various directions, squeezing and pulsating against his frame.
Optimus spike sprung out of its casing, fully erect, already dripping with lubricant.
Megatron's optics went wide.
"We-he-hell, then. How come you get to have all of the fun?" Ratchet asked, an evil glint in his eye. "Primus come and take me." Megatron looked at Ratchet, slightly aback, but Megatron found that his own spike betrayed him - watching Optimus wrapped up in tentacles, moaning, was a wet dream that he had never expected to have.
"If you wa-AAH" Optimus' comment was interrupted by a final tentacle - noticeably hollow, sliding down around the length of his spike, squeezing down on it with pulses that began to urge an imminent overload from the Prime's frame. The tentacle pulled back - just the tip was covered, and tiny filaments just behind the head of the tentacle whipped back and forth against the head of Optimus' spike. It squeezed, tighter and tighter, until Optimus' spike almost threatened to pop out, then slammed down the length of Optimus' spike again. It pulled back just as quickly, and thrust again over and over.
Optimus' optics rolled back into his helm, lost in the pleasure and the sensation. Lubricant dripped from the appendage, and it pushed all the way down, holding, the head squeezing as hard as it could. The pressure on his spike slide up its length, clamping down in a small ring that soon brushed up against the head of his spike - as it worked along to the tip, Optimus' entire frame reflexively tensed - and the pressure began at the bottom again, without a moment for him to relax.
The process repeated again, slowly, methodically, gradually building in speed - mimicking the sensation of an overload from the outside. Overload was very rapidly on its way for him, and Optimus felt no shame in relieving some of the pressure in his system with loud moans - every time the pressure wave reached his spikehead, one escaped his vocalizer.
Every time the pressure wave reached his spikehead, his entire frame tensed up, tighter and tighter. Optimus took the moments he had while the rest of his shaft was squeezed to relax that tension, but eventually, there was no escape - no turning back.
Something inside of him clicked, and two waves later, just as the wave passed over the edge of his spikehead, Optimus overloaded, loudly and forcefully. The tentacle immediately shot back, rubbing itself along his spike, milking him for every ounce of transfluid it could gather. Optimus let out several more cries as it continued to rub his hypersensitive tip - it was too much, but he wasn't getting let go.
Eventually, after what felt like an eternity, Optimus found himself being lowered, back onto the ground. Vents roaring, frame drained from the drawn-out overload, he righted and focused his optics before sitting up, and noticed that his trinemates were in similar positions.