To those who did not know her, it would be easy to assume that Princess Celestia, diarch of Equestria, had very little to worry about in her life, save for the daily drudgery of ruling the kingdom. But that, naturally, was never truly the case, as there had been many times when the ruler of the sun had been required to help in times of need. And while many of Equestria's more recent crises had been quelled thanks to her former student, Princess Twilight Sparkle, there were still many days when Celestia took to the field herself to sort out whatever issue might befall her nation.

And so it was that today, she was flying through the skies of Canterlot, Equestria's crown jewel, at full speed, for word had reached her ears that there was an intruder in the city. When an outside force had last entered Canterlot, the populace had been driven into a panic, and she was not about to let that happen again. So, she deigned to deal with this matter herself, and was heading straight for where the newcomer had supposedly been apprehended. It was not long before she caught sight of a familiar face, also flying above the city. Princess Luna, her sister.

When the elder alicorn was within earshot, the Princess of the moon spoke to her.

"Tia! I'm glad you came. I was unsure of how best to deal with this."

Celestia nodded at that.

"What happened exactly?"

Luna pointed to the ground before speaking.

"The report said there was some sort of magic, a bright green vortex of some sort. And a...creature came out. The guards have their eye on him."

Celestia looked down to where she was pointing an narrowed her eyes.

"No need to worry, Luna. We can deal with this matter together. But first, let's head downwards."

Luna nodded in agreement and the two sisters began flying with all due haste towards the ground of the city. With extreme grace, their hooves landed, and they took a few steps forward towards a group of assembled royal guards, all while Celestia was looking around the area for this mysterious intruder.

"Alright, where is he?"

Celestia looked on as Luna walked past her and towards the guards. She soon stopped and turned to face Celestia, before stretching out a hoof to point to something nearby.

"Well...here he is."

It was here that Celestia brought her full attention to an object that, until Luna pointed to it, she hadn't given much thought to. It appeared to be a vehicle of some sort, and at first glance, a pony might mistake it for a locomotive, not unlike the ones used to travel around Equestria. But this was a design unlike anything Celestia had ever seen. It was much larger for one thing, was far more angular and was painted the brightest shade of red. In the front there were two windows, behind which was presumably where the driver went, though Celestia could not see one. With a look of confusion, she turned to her sister once more.

"Is he behind this...thing?"

Luna shook her head.

"Not exactly."

Celestia tilted her head at that, clearly confused by what her sister was talking about. Seeing this expression, Luna sighed before walking over to the massive vehicle, raising a hoof and gently tapping it on the hood of the thing.

"Um, Sir? My sister is here, like I said."

Under normal circumstances, Celestia would be quite concerned that her little sister was speaking to inanimate objects. But that worry vanished in an instant as the vehicle began to move under it's own power. Celestia, Luna and the guards all took a step back as the massive machine began, to the shock of Celestia, change shape. Individual pieces would break apart, withdraw into itself, new pieces would emerge from within, some would fold into new sizes and all the while, it was taking on a brand new form.

After watching this amazing display by the machine, Celestia stood in awe at what now stood before her. It was a moving creature, but one of metal, rather than flesh and bone. It stood on two legs, not four like the ponies, and was unlike anything Celestia had ever witnessed in her long life. It's torso and arms were that same bright shade of red, while it's legs were a dark blue. It's heard bore a similarly-blue helmet of sorts, and it's eyes glowed a far lighter shade, with it's mouth covered by a grey metal plate. The elder sister looked at Luna with uncertainty in her eyes, and one nod from the latter made it clear that she'd had a similar reaction already.

But it was now that this strange creature began to move forward, and Celestia stood her ground, not wanting to show weakness. But, rather surprisingly, this giant made no aggressive moves towards her, instead taking a kneeling stance, brining it's head closer towards her. There was an uncomfortable silence as Celestia looked into it's bright, blue eyes, before this being finally spoke.

"Greetings, Celestia of Equestria. I am Optimus Prime."

The voice was deep, and somewhat gruff. The kind of voice one would expect, not only from someone very old, but one who had experienced a great deal. However, what took Celestia's interest was that this person knew her name. Stealing a glance towards Luna, the younger sister nodded, confirming that it had indeed been her that had told this Optimus of her. So, clearing her throat, Celestia assumed her usual, regal stance before addressing this newcomer.

"And greeting to you Optimus Prime. I must confess, I have never encountered one such as you. May I ask where you are from?"

The red and blue giant nodded before speaking.

"My race hails from a world known as Cybertron, a place inhabited by others like me, autonomous robotic organisms, or "living machines" as some might call us."

His eyes then showed a brief glimmer of hesitation before he carried on.

"But it is not that world from which I found my way here. Not long ago, I was upon another world, called Earth, the home of a race known as humans."

Celestia's ears pricked up upon hearing that.

"Humans? As in two legs? About my height?"

Optimus' eyes widened in surprise at that.

"Yes. You know of them and their world?"

Celestia nodded. It was not long ago that Twilight, having only recently been made into an alicorn, had journeyed through a magical mirror to another world. Even Celestia did not know what would be on the other side, so Twilight's reports upon her return were incredibly informative. By the descriptions she'd been given, it would seem that this was the world Optimus was speaking of. And if that was where he came from, she felt obligated to at least tell him of this.

"One of my people once went to that world by way of a gateway we have in our possession."

Optimus looked at her, as if trying to see if she was speaking truly. When he saw that there was no deception in her face, he nodded.

"Then perhaps my being here is not as much of a long-term prospect as I thought."

It was clear from those words that this new arrival would now wish to use the magic mirror to get himself back to the world of humans. However, there was one very important matter in that regard that Celestia felt he needed to use.

"I would gladly allow you to us it, Optimus. However, it only works every few years. And even if it was working, I doubt the doorway could accommodate your..."

The Princess then looked Optimus up and down, taking in his great bulk.

"...sizable needs."

There was a brief moment when Celestia could have sworn that there was confusion on Optimus' face. However, once her words sunk in, that expression changed to one of understanding, and he game a silent nod. It was obvious that he was becoming increasingly concerned that he would end up stranded in their world, something that Celestia did not wish him to feel. However, her attention was then drawn to a group of Canterlot citizens, who had gathered nearby, clearly in awe of Optimus. Although she understood their reaction, the last thing she needed was for her people to start gawking at him like he was an animal at a zoo.

So, giving a nod to Luna, she watched as her sister led the nearby guards to try and keep the crowds back, before she turned her attention to Optimus once more. For there was a question on her mind that she needed to know the answer to.

"You say that you were in the world of humans before coming here. But how did you get here, exactly?"

Optimus watched her in silence briefly before explaining.

"My people have a technology at our disposal, which allows us to travel great distances within moments. I was heading out on a routine scouting mission when there was a malfunction. Instead of sending me to my intended destination, it brought me...here. I can only hope that my team are able to rectify this error."

Celestia nodded at that. This technology of which he spoke must have been the "magic" that Luna said was reported. Clearly no magic was used here, though the idea that technology could achieve something akin to the teleportation spell, that she and other high-level magic users could call upon, was a fascinating prospect. However, it was here that something Optimus said gained her full attention, and she looked at him with uncertainty before speaking.

"You were on a scouting mission? Are you a soldier?"

Optimus' expression changed once more, but this time to one Celestia recognised immediately as sadness, before he gave the Princess her answer.

"Not by choice."

Those words were all Celestia needed to hear to know that this person had been through a lot. Part of her wanted to leave things be, and not to pry where she might not be wanted. But, this was a being that her world had never seen before, and her curiosity got the better of her as she stepped forward and spoke.

"Are you...fighting a war?"

There was a brief and uncomfortable silence as Optimus regarded her for a while, but he soon let out a sigh and gave a slow nod before speaking.

"Yes. Though it is one that began long ago. My world was once peaceful, but like all great societies, discontent emerged, and from it was born a group that started a war which engulfed my entire planet. A war that has gone on for countless centuries."

Celestia stood aghast at what she was hearing. Although soldiers were not unheard of in Equestria, as the nearby royal guards proved, the idea of full-scale conflict amongst ponies was a thing of the ancient past, from the times when the three tribes were still divided. It was something she was always thankful for, that those in her nation had never experienced the horrors of such conflict. That there was a world out there whose people not only fought each other, but had done so for longer than she had been alive, was a terrible thing to consider, and one she hoped her people would never have to endure.

But her attention was brought back to Optimus in earnest, as he briefly looked away from her with a look of deep regret upon his face.

"Worse still...the one who led our enemies, was one I once considered a brother."

His eyes narrowed and his face became clearly pained.

"Of all the thing that have happened in my life, there is nothing I regret more than the fact that my deadliest enemy...was once my dearest friend."

It was here that Celestia gained a similar look of sadness upon her face. Optimus was deep in thought at this point, and thus she had the opportunity to look over her shoulder, gazing upon Luna, who was still busying herself with keeping back the other ponies. Prime's words had hit quite close to home for Celestia, as his story was not unlike one she knew all too well. As memories of a thousand yeas past resurfaced in her mind, she let out a sigh.

"I know the feeling."

Turning back to face Optimus, Celestia saw that the latter now had a look of curiosity on his face, having quite clearly heard what she'd just said. Composing herself once more, she cleared her throat before speaking.

"It must have been hard, all that fighting."

Optimus nodded response to that remark.

"Harder than I can ever describe. Although, there was a time when the life of a warrior was the most foreign notion in the world to me. For I did not start out as a soldier, but as an archivist."

Celestia raised an eyebrow, having been taken aback by those words.

"Archivist? You were a...librarian?"

Optimus nodded yet again.

"It was another life, but yes. Had our world remained peaceful, I'd have been content to stay with my history records and research. Fate, it seems, had other plans for me. And though I would not have chosen it, my journey led me to become a leader for my people."

Upon hearing that, Celestia became thoughtful for a moment, before, to Optimus' surprise, she took on a small smile and gave a brief chuckle. The metal giant raised an eyebrow at that, prompting Celestia to raise a hoof before explaining herself.

"Sorry, it's just...you remind me of a former student of mine."

The look on Optimus' face made it clear that he would have liked to enquire further about that, but both he and Celestia were interrupted by a blinding flash of light nearby. Assuming that danger was nearby, Celestia spread out her wings in an intimidating gesture, as did Luna and the nearby guards. But, the sun Princess' eyes widened as she looked upon what now there. It was as the reports described, a swirling vortex, composed of bright green light. Turning, she looked upon Optimus, who was now standing tall once more. The Cybertronian took a few steps forward, clearly wary of the re-emergence of this doorway.

Celestia followed, equally wary, but stopped as a new and unfamiliar voice called out from within the vortex.

"Optimus?! Can you hear me?!"

Celestia looked on as Optimus took another step forward, his eyes now wide with surprise.

"Ratchet?"

The voice answered back immediately.

"Thank the Allspark! We thought we'd lost you!"

Optimus turned and looked down at Celestia, as the Princess noted his expression of relief. It seems that his stay in Equeastria would, as he once feared, not be long-term after all. The Prime then turned back to the portal.

"What is the situation?" he asked.

"The space bridge has been repaired, but it won't stay open for long. You need to come through, now!" the voice replied.

Before anyone else could say anything further, another voice, deeper this time, came from within the portal.

"Come on, Boss! Things have been pretty bad without you. We're practically falling over our own-OW!!!"

There was a sudden, and very loud, sound of clanging metal from the other side of the portal, leading to Celestia and Luna looking at each other with both confusion and bemusement, before the deeper voice spoke out again.

"Um...oops."

"BULKHEAD!!! I NEEDED THAT!!!" the other voice shouted.

Ignoring the as-yet unknown bumbling of his colleagues, Optimus turned to face Celestia, his face one of uttermost seriousness.

"It would appear that this is where we part ways, Princess."

The sun Princess looked upon him in an almost sad manner.

"It's a shame you could not have stayed longer. I'm sure our people would have loved to meet you."

Optimus gave a brief nod at that.

"And I would have been equally pleased to make their acquaintance. Though I lament that my time here has been brief, I take solace in the knowledge that, in this vast universe..."

For a brief moment, Optimus stopped and looked up from Celestia, to gaze upon his surroundings. The pristine and unblemished spires of Canterlot, and the calm yet beautiful weather and landscape around the city. He let out a long sigh before looking down to face her yet again, saying what he truly needed to say.

"...there is at least one world untainted by the darkness that has plagued both mine and Earth."

Celestia gave a brief look over to Luna, who simply shrugged her shoulders, before giving her full attention to Optimus once more. She didn't know if he meant what he'd just said, or said it simply to put her at ease, but regardless, it was a fine sentiment, and one that deserved a proper response. And so, before speaking, she found herself bowing her head in respect to him.

"Then I bid you farewell, Optimus Prime."

The titanic visitor stood tall and gave a similar bow to her in response.

"And to you, Princess Celestia."

With the formalities over with, Optimus faced the portal and began to run towards it as fast as he could. Celestia and all who were gathered there looked on as he became engulfed in the portal's bright green light, before there was yet another blinding flash. The assembled crowd, as well as the two Princesses, covered their eyes briefly before the light died down, at which point they saw that both the portal, and Optimus were gone. With that rather monumental occurrence now over, the guards began to hurry the crowds away, the latter of which now busied themselves with excited chatter over what had just happened.

Meanwhile, Celestia and Luna just stared at the spot where the portal had been, and after a long silence, Luna broke it.

"Well...what do you think?"

Celestia considered her words carefully, thinking over everything she'd learned from that remarkable visitor to their world. After a brief moment, she broke into a small smile before answering her sister.

"He was...most impressive."

Luna stared at her sister's expression for a few moments before a mischievous smirk appeared on her face.

"Why Tia, if I didn't know better, I'd say you were rather taken with our brief guest."

Celestia chuckled at that before replying.

"Nonsense, Luna. Besides, I doubt it would work."

Luna nodded for a moment at that.

"Maybe, but I'll bet it'd be nice for you to be in a relationship where you're NOT the oldest one in it for once."

Looking towards Luna, Celestia's expression was one of both annoyance and amusement.

"And this is exactly why love is Cadence's job!"

Author's Notes:

No joke, but I actually started thinking in Optimus Prime's voice by the time I'd finished writing this story.