Hopefully I've addressed the sparkling/pod thing that Starscream was struggling to get to work in RotF in this chapter. Also, this is an angst fic.

Only a Prime

Chapter 2

- One year later –

Optimus examined the new component from all angles where it hung suspended in milky yellow fluid – energon diluted to keep the absorbent metals alive. It looked too small to have taken a year to construct, but now the diamond shaped chamber was finally ready for grafting. Ratchet entered the Medbay without ceremony, moving to the operating berth and beginning the final preparations for surgery.

"The Peterbuilt's in the main hanger. I'll have it brought in tomorrow when we're done so I can check your re-configuration scan." When he received no response, Ratchet paused in his preparations and looked to the mech by his workbench. Optimus was considering the chamber with dim optics, lost in thought. He came to stand alongside the taller mech, arms folded, and murmured, "Last chance to change your mind, Optimus."

A soft sound, almost a sigh, before Optimus produced a small cylinder from a shoulder hatch and held it out to the medic. "I'm ready if you are."

Ratchet nodded, scanning the contents of the container through his fingers as he carried it across to the berth. "My sample's ready as well. I'll prepare them after the chamber's in place and energise the mix. A jolt through your spark should do the rest. We're likely not going to get another significant window for recovery and observation, so it'll have to be two paradigm shifts at once."

They'd gone through the procedure a dozen times in detail, but Optimus found a diminishing comfort in the knowledge as he moved to sit on the edge of the berth. It took several minutes for him to collapse away his armour into subspace, leaving him in naked protoform for the first time since landing. This was to be a change in his fundamental being, so base that he needed to be online to consciously adjust to the change lest he go into complete system shock upon awaking to it. He lay back and settled his limbs, optics soon drawn back to the suspended chamber.

"This will take three to four hours." Coming to stand at his side, Ratchet began to feed fine transparent lines into the mech's limbs. "Removing the protomass will be very quick, as opposed to transplanting the chamber. We'll need to keep conversing throughout, and I'll be commentating on what I'm doing, as I'm doing it, and you must listen and understand. This is as much a psychological operation as it is physical."

"I understand," Optimus murmured, optics fixing on an indistinct point on the ceiling as the last monitoring and regulating connections were made. There was a pressure against the juncture of his right shoulder that turned his body heavy and numb, deactivating his pain receptors and motor functions. They were ready. He heard the medic's hands transform and kept his stare on the overhead lights.

"Making the first incision over your spark chamber," Ratchet dictated flatly, as if lecturing abstractly as opposed to coating his hands in energon breaching the protoform's covering. Thin black tubes flexing from the undersides of his wrists provided suction, actively scanning the fluid for abnormalities before it was stored in an isolated internal tank to be disposed of later.

Ratchet had long become used to working without an assistant, but there were some procedures that newly highlighted how severe that lacking was. He'd done the best he could in having everything readily close to hand, but now he could only be wary and hope Primus approved of this plan.

"I'm beginning to remove the required half-tonne of protomatter directly beneath, cauterising actively." The cut in the thin, skin-like sheath was pulled open and pinned in place to leave the wound gaping, glistening silver and secreting energon.

Carefully razing away inches of protoflesh, Ratchet didn't look away as he asked, "How are you doing?"

The Prime could feel pressure and tugging, but no pain and certainly no sensations that would suggest that chunks of his body were being cut out. "I'm well," he replied softly, optics shuttering as he tried to guide his processor away from imagining the wound being bored out of him. He understood that it was important to remain aware, but he did not want to actively picture the procedure as it was being performed and described. "What explanation did you give for my time off in the end?"

Ratchet didn't respond for a full minute, optics bright with concentration as he cut deeper into the silver flesh. It came away in slab-like chunks, blackened and coarse from the cauterizing heat of the laser. "I blamed it on your resurrection bringing you back but not fully undoing all the damage that led to your death. Not a wound, exactly, but an abnormality in your protoform that requires significant enough surgery to necessitate rescanning an alt form and keeping away from combat for a few days."

A soft sound. "I notified NEST that I would need six days to recuperate fully, but I did not go into any specifics." He onlined his optics and immediately saw Ratchet lifting away a glistening piece of protoflesh. It made the mutilation they had been planning for months real, and his soft vents exhaled shakily. As much as he wanted to, he couldn't look away from it. "Lennox is going to request that the Autobots have access to the facility in the Hoover dam where the All Spark was held for additional protection."

Ratchet smiled a little, dry and faint as he added to the growing pile in the tray. "Having you laid up is very nearly a national emergency for the humans, especially if the Decepticons somehow get wind of it."

It would have been impossible to carry this out without taking Megatron into account. They had waited weeks for a significant enough skirmish that would leave the Decepticons licking their wounds for a few days, giving Optimus a window of inactivity for the post-op recovery.

"Ironhide's outside," Optimus remarked softly, finally dragging his optics from the material Ratchet was lifting away.

The medic hummed. "Yes, he followed me from the Yard. I won't be surprised if he refuses a guard rota and stands outside that door until you're discharged."

"Will he be able to detect anything?"

"Not until the sparkling has grown large enough to become obvious as an energy reading." Ratchet paused in his excavations to focus on draining the leaked energon from the site, micro-sealing the breaches with brief, sizzling touches. "For the first half of carriage, it'll be an integrated part of your systems and without any isolating features. After that, its processor will begin booting up and experimenting with motor functions and the like, and then we'll have to tell them."

Optimus felt a pang at that, and suddenly wanted more than anything to be able to move his arms to rub his optics. From the neck down he was completely paralysed, and would remain so for several days until Ratchet was satisfied with the condition of the incision. In that time, he'd see no one but Ratchet lest a visitor glimpse something incriminating or bring in a contaminant that would take disastrous advantage of his exposed state. Ironhide, his bodyguard since he'd been made a Prime, was standing as close as he could get.

"Alright, I've cleared the space and prepared it for grafting," Ratchet finally uttered, breaking his thoughts as he set aside the tray of detritus. "I've neutralized the self-repair nanites in this area so that they won't re-generate your natural protoflesh and corrupt the gestation chamber."

Irreversible. His body as he'd known it for millennia was altered. Soon he would be the first Prime able to bear new life, and that too would be irreversible. Whether they were successful now or not. Optimus waited silently, blinking in a flinch when Ratchet touched his helm and came to stand at his shoulder.

"Ready?" At the breathed affirmative, Ratchet crossed to the workbench bearing the precious cylinder and took a high-sided tray from the drawer beneath. "You must keep talking to me, Optimus. It's critical that you remain cogent and aware of the changes as they take place."

A snapped retort curled on his glossa, quickly suppressed as Optimus fought to temper his emotions. Ratchet had built a gestation chamber and cut a hole in his body, and was about to seal the chamber inside and spark him. Everything was going to change. He had no hesitations with going through with it, but this anxiety hadn't been present whilst they were speculating about a procedure that would in the future.

He shunted an exhale. "The chamber is alive already," Optimus uttered quickly, optics tracking across the imperfections in the sloped ceiling. "Why can't it support a sparkling outside of a body?"

"If we knew the answer to that, our species wouldn't be borderline extinct," came the flat reply as Ratchet broke the seal on top of the cylinder and gently lifted the contents out. "In theory, it should work: saturate the chamber with energon and compounds, regulate pressure and temperature to stimulate growth, and keep the fluids charged. But in reality, the sparklings starve to death. We can't simulate the influence of a carrier's systems any more than we can identify it. One of life's mysteries."

"Will my systems adapt?"

The medic returned with the tray bearing the chamber, setting it down on the berth beside a long thigh. "They should do. I've been flooding you with the electrolytes for months. Speaking of which, I'm going to give you something before I begin implanting the chamber. Extreme nausea is a side effect of it, but I've got a regulating line in your tank so there's no risk of you purging. Just concentrate on my voice and it'll pass in a few minutes."

Optimus said nothing, seeing more than feeling the needle pressing into his chassis above the gaping wound. Scant seconds passed before it felt like his equilibrium sensors had been thrown into his fuel tank and shaken violently. He closed his optics and gritted his dentals, but it didn't help. "How long until we know?"

Ratchet cradled the chamber in both hands, dwarfing the deceptively delicate-looking structure as he lowered it into the weeping vacuity. "I'll put eight potentials in the chamber to increase the odds, but it'll be at least a day before we know if any of them have attached to the lining and begun absorption."

Though entirely numb, Optimus had the strange sense of being able to feel the new organ as its weight settled into him, lining up with his raw protoflesh. It made the nausea overwhelming. He felt the space around his spark tighten sharply before the regulating line intervened and forced it back to a normal rhythm. Suddenly, and from nowhere, he wished that someone else was here – someone who was neither being irreversibly disfigured or doing the disfiguring.

"What if more than one latches?" he asked, needing the distraction of a voice.

Ratchet's optics flickered up from arranging the chamber, pressing fractionally on the pliant metal to line up connections and begin the long process of micro-welding them shut. "The weakest ones get aborted. Carrying one sparkling is going to be pushing the limits of your body and my expertise. I won't tempt -"

The medic cut himself off when one of the monitors flagged a silent alarm, his scanners fixing to the site before his optics had moved. Leukocyte analogues were swarming past the area he'd neutralised them in and were converging on the wound to attack the chamber. He felt Optimus watching him, though there was no way that he could be aware of the alarm aside from his behaviour. "I'm going to have to give you another dose to avoid a problem. There's nothing to worry about."

Optimus didn't have time to respond to that statement before the needle was reinserted and a fresh, curdling swell crashed through him. He sincerely wanted to purge just so that the feeling might pass. Ratchet's hands returned to their work.

Quiet fell between them for a long time whilst Ratchet concentrated and Optimus listened. Hearing was somehow worse than seeing what was being done, and it made him keen to keep Ratchet talking over the wet noises. Close to the end, when only a dozen minor structural reformats remained to do before the chamber was ready, Ratchet stepped away from the berth's edge and came to stand at his helm.

"I'm going to put you into recharge once the breach is closed and give your systems some time to adjust," he explained softly, noting with a frown the dark edges to the optics fixed on him. Sending a command to increase the charge on the energon he was feeding in, Ratchet began a quick scan at the same time he rested his knuckles against Optimus's jaw – one of the only places the mech currently had feeling in. "Tomorrow, if everything looks okay, I'll implant the zygotes and shock your spark to bud with them. I'll keep you under for that, as well."

The nod was implicit. "So, hopefully, when I come back online..."

"Hopefully," Ratchet affirmed with a soft smile, his face plates drawn. His expression shifted into something between reassurance and earnest, his hand moving fractionally to stroke the slender jaw. "But if none of them take, we just try again. For as long as you wish."

A whisper of a sigh and Optimus shuttered his optics briefly, wanting this strange and troubling period of transition to be over. "Thank you."

Ratchet harrumphed without feeling, stepping back to the wound and beginning to make the final adjustments. "I'm not the one making the sacrifices."

"But you are implicated," Optimus replied flatly, though kindly. The nausea had almost entirely passed now, and if he hadn't been connected to so many monitors ad regulators he'd have fallen into an exhausted recharge cycle. Instead he listened to the subtle movements of Ratchet's hands in his chassis, uttering a silent prayer to Primus to allow a new life to emerge from where they lay.

This is quite a big deviation from my usual "mpreg-style", so it'd be really good to hear how you're finding it.