Scratching my mechpreg itch with this one, as well as having my first go with 'sticky' biology for the Transformers. Warnings for angst in later chapters.

Only a Prime

Chapter One

It was a phrase that recurred throughout Cybertronian lore, now lost with the destruction of the All Spark. Only a Prime could defeat the Fallen, and Optimus had had to be resurrected as the last one to do it. There was no telling what else lay ahead that only one of his line could affect. More than that, the Primes had stood since antiquity as symbols larger than themselves: encapsulating an ideal, an archetype, a single-minded commitment to safeguard life and liberty throughout the universe. Optimus professed to the Autobots that he was just another mech - last to be attended by Ratchet if others needed him more, and first into battle no matter how unfavourable the odds. But he was also a Prime, the last, and he had died once already. Next time, fate might not be so kind.

Optimus had led Ratchet away from the Diego Garcia base to speak, miles into the clear desert where even Ironhide would not hear of it. What he proposed would change everything, had done by its mere suggestion, and now he watched the medic's back where he stood agitated and thinking. He'd made his case, argued his side, and now he waited to see how much more pushing he needed to do to get his long-time friend to agree despite his great reservations.

After twenty minutes of silence, when the sand being stirred into his vents began to become irritating, Optimus finally approached the medic. "I know it is asking a great deal, but it is my choice, and for the good of us all."

Ratchet turned partially to meet him with bright optics. They shuttered briefly, weary, before he shifted his feet to face the Prime entirely. "The risks involved," he began, trailing off with gritted dentals and averting his gaze.

It occurred to Optimus that this level of cautious protectiveness regarding his safety had increased after the Fallen. After the forest. The reminder that, despite his value as a Prime, he was still a mortal mech had shaken the Autobots, and there was a growing belief that it made more tactical sense to shield him from danger than to try to end the war quickly. Optimus was staunchly against this, but it had underlined the point: there could not only be one.

"The risks are to me alone, Ratchet," he reminded softly, speaking beneath the medic's sharper tones. "I have almost passed into the Well once already, and will do so again, permanently, at any time. Without the All Spark, a new Prime spark cannot be kindled. But with my own-"

"This could fail at every turn," Ratchet cut in, and realized the moment he'd said it that he'd already laid the foundations in his processor to agree. It was nigh-impossible to deny the Prime when he had his spark committed to an idea. It was why he had led them on the losing side for so long, and why they'd stayed to protect the humans though the order to had died with him. And it would be a greater blow to the Autobots in the future to have lost the last Prime, as well as Optimus himself.

Brushing a hand across his optics, Ratchet spoke into the heel of his hand, trying to stop his processor from visualising the disastrous variables. "If I could stimulate your spark to bud a strong enough haploid, it would need to gestate as a normal carriage, and there is a reason why Primes have been made, not born. The power they demand will decimate a normal femme."

Optimus nodded fractionally, and his voice was even. "Which is why I have decided to do it myself. You can build a gestation chamber, and given enough time, there's no reason why you couldn't find a way to graft it onto my systems."

Ratchet huffed through his vents with a low sound, arms folding stiff across his chassis. "No reason, my aft. Replacing a gestation chamber is one thing, but building one for a system that has no business being connected to it is another entirely. I'd need to install all new feeds to your spark casing, new assimilation protocols for the physical growth, rearrange your systems so that we can get the thing back out once it's grown, and then there's the rest."

Behind the face plate, hidden from view, Optimus's mouth pulled into a thin, almost grim smile. "But you can do it."

A beat before the medic shifted his weight in the sand, sighing. "Given the time, and against my better judgement, yes."

"Thank you, Ratchet. I know this will be difficult for you, for us both, but there is no other way," Optimus affirmed, touching a hand to the shorter mech's shoulder. When he began to draw his hand away to begin returning to the base, Ratchet's fingers closed about his wrist.

"I'm good, but I can't work miracles," Ratchet went on, more strength in his words as he fell back into his usual acerbic tones. "This can't be an immaculate conception. You're going to need another bot."

Optimus shifted his hand so that his thumb crossed into Ratchet's palm, squeezing once before drawing his arm back. "I was going to ask if you would consider being the other creator." The naked emotion on the medic's face to that statement suddenly brought forth a wave of awkwardness, and it was an effort to keep holding his gaze. He couldn't entirely suppress the sigh through his vents. "Anyone else's judgement would be clouded if they knew I was carrying, let alone if it were their own offspring, and that will cost lives in battle. You have long been able to partition your emotional attachments from your job, and, I need the other creator to be strong."

Ratchet arched a brow, his voice dry and not belaying any of the myriad of feelings clamouring for dominance in his spark. Honour and anxiety were both close to the top. "And you want as few to know about this little gambit of yours as possible. That is, just us."

It wasn't automatic, but the retraction of his faceplate was triggered by something instinctual; some sense that a gesture of openness to the extent of vulnerability was appropriate and, perhaps, required at this moment. There had never been any intimacy or desire between them – only a mutual respect and platonic kinship. Optimus chose his words carefully, but with a privately reassuring ease. "You are one of my oldest friends and comrades. It would gratify me to create a new life with you."

Another pause as Ratchet moved a few paces forward to stand alongside Optimus, though facing the other way, towards the base. Even with a gestation chamber, they were both mechs, so interfacing to conceive wasn't a possibility – and he wasn't going to begin speculating upon the unnecessary and psychologically treacherous route of installing a valve. No – it would be entirely clinical, conducted more in the lab than in a berth, which stunted that potential awkwardness. And Optimus was right about his ability to disassociate from what needed to be done.

But still, it was an enormous commitment, even whilst strictly platonic. "It'll take months for me to gather the right materials let alone build a chamber. There's no reason why during that time you couldn't court-"

Optimus held up a hand, the flicker of pain in his features visible purely because of the absence of the mask. "This may not work. It's dangerous, and a great deal can go wrong at any time." He paused, cycling a breath. This idea had been on his processor from a few weeks after returning from Egypt, and the worst case scenarios for almost as long. He didn't want Ratchet to think that he hadn't considered the worst as well as the best when formulating this plan. "I can face these trials, but I fear that I'm not strong enough to support another as well. You can be impartial."

Ratchet considered that with as much honesty as he could. It was the Prime's gaze that solidified his decision in the end, and he nodded with a sigh. "Alright. Alright, we'll try."