So this one's a bit of an interesting prompt. Given the nature of one of the AUs that I've created, I thought that it would be a great opportunity to tackle this part of the boys' history together.
So, this is set back in my Fae/Urban Fantasy AU, but we aren't going to 1917, but rather, this is a prequel to the story I created, and it answers the question: How did Holmes and Watson discover they were Paired?

To give a timeline… let's say this is some time between 'The Adventure of Silver Blaze' and set around 'The Adventure of the Solitary Cyclist,' so assume 1895.

I do, unfortunately, have to sneak in some angst here, given the nature of the canon story, but this is predominantly focused on the friendship/relationship aspect.

This is a two-part adventure! I have a lot I want to do with this AU, so I want to give it two chapters like it deserves. However I will more than likely be doing another prompt for the next chapter, so we'll be back in this AU for Chapter 4.
And with that out of the way….

From Ennui Enigma: Fairies

And

From Ennui Enigma: An inexplicable feeling

Summer and Winter Paired

In my association with the Winter Fae Lord, Sherlock Holmes, I had come to realize the relationship between the Summer Court and the Winter Court, their squabbles? Were often for naught.

The tales that the Summer Court would spin about the Winter Court preying on the warmth and life of summer paled in comparison to reality, even if it was just Sherlock Holmes.

While he was, by my accounts, still a Fae of logic and rationality, he was a Fair Folk with a great heart. I longed to go back and shake the past John Watson for believing in such things.

If I did not know better, Holmes might be a long-lost Summer Court Fae. How else could one explain it when he was the one to tend to my old wounds, soothe my nightmares with the help of his violin, or even easing the most frantic of clients?

Nowhere was it better displayed than during our encounter with Violet Smith, which I have promised to recall here for a missive to Mycroft Holmes, still embroiled in Winter Court Politics.

Violet Smith had come to us with a bizarre case, although Holmes would be more inclined to call it singular and intriguing.

For he did not know of any mortal men who'd want to cycle after a young musician on lonely country roads rather than approaching her head-on to confess their feelings or thoughts of affection.

Such was the case, indeed, given that she had also revealed some of the success in her musical work came from the fact she had Siren heritage, through her mother.

And given that Violet herself said she has enough control over her Song that it wouldn't be mesmerism, it could not be a simple lover.

What went unspoken, however, was that the more Holmes spoke to and got to know young Violet Smith, he'd developed a fierce protectiveness of the girl that I had seen him do before for Miss Mary Sutherland, the half Summer Fae woman that her stepfather had duped into dating a 'Hosmer Angel,' Violet Hunter, the bold human that had gone into the Rogue Fae Dwelling, the Copper Beeches and remained unscathed, and Helen Stoner, another human that had been tormented by her vampire stepfather, Doctor Roylott.

It was an admirable quality of his, as it always will be. When Violet returned to inform us that she would be leaving Mr. Carruthers' employ, Holmes had been reluctant to let her go, though almost near joy when it meant that she would be out of the hands of him and his ilk.

That being said, he still wears the scar on his brow with such pride! I can't say I've seen him preen at his expression like this before.

"It's not every day I get so much exercise, and it was delicious, Watson." He'd said.

Now? We'd received a spelled telegram that detailed that Mr. Carruthers had gotten a horse and trap so Violet should be able to return to her mother rather than stay longer.

"All my troubles will be over on Saturday… Saturday, Holmes, do you think this is all over?" I asked as Holmes took the pipe he'd been smoking out of his mouth, brow furrowing.

"I would need more data, my dear Watson, but… we should accompany and follow her on this journey to see that she doesn't come to harm." Said he, the slight Winter Fae snarl coming to life in his voice.

I can not blame him either. As much as I have said that Holmes has grown fond of her, I have too.

And it would wound me as profoundly as any physical wound if harm came to her.

"And why does that word worry me?" Holmes added, placing his pipe down.

"What word?" I asked, watching as his expression tensed, lips twitching.

"Trap," Holmes said. "Horse is well and fine, but… trap."

Indeed, trap was an ominous word. Holmes and I had gone into the countryside, intent on making sure that Violet would travel unharmed.

It was a beautiful Spring day, and despite the apparent alarm that hung between us, I could not help but enjoy the Elements at work.

If this were back at Baker Street or in any of the Public Houses that host those who Crossed Over, I'd let my wings out for a spell. But now isn't that time.

"What a beautiful day, Holmes!" I called. "Who would consider hurting a girl on a beautiful day like this?"

"I don't know quite yet!" Holmes called back, pulling out his field glasses. We both leaned in as the tiny dot of Violet Smith and her driver crossed the landscape, but—

"They're early." Holmes and I glanced at each other with growing horror. She had gone early, and there was no chance we would be able to tail them.

"And we won't be able to intercept our villains if they're behind them," I added. "What should we do?"

"We can run." Holmes and I took off across the countryside, almost instinctively dropping the glamour spells we'd been keeping up around each other as we leaped over fallen branches and towards the road where we'd seen Violet.

I do not like where this is going!

We'd reached the road, when, as soon as we stopped, a horrified scream pierced the air—

And Violet Smith was nowhere to be found, her trap and horse barreling towards us empty.

"I should have been here sooner! Watson, it's abduction, murder, Elements know what!" Holmes snapped as he pointed to the horse. "Watson, stop that horse!"

While I did just that, the strangest, most inexplicable feeling washed over me as I brought the horse to Holmes.

There was a sudden chill, but only localized to my body. As if Winter and Summer are… together?

I glanced up, noticing the golden magic that normally wreathed around me(and remained hidden at Baker Street) had reached out… and was twining with Holmes's ice-blue magic of the Winter Court.

It was a strange feeling, like an extra limb, reaching out and holding hands with someone else's hand, even if you did not do any of those actions. But more so?

It feels like returning home, like it is right. Or that Holmes is an extension of myself, or I am of him. That we're whole again. It was a lovely feeling, bubbling against the hollow of my throat, despite my sudden fear.

"Watson." Holmes's anger had simmered; how did I know that? As he crossed the ground to join me.

"It seems we two have been Paired." Said he, both of our magics greeting each other as if they were old friends reuniting once more. Blue and Gold drifted over our heads, following each other, and clasped tight. "Instead of my magic lashing out in anger, my dear fellow, it sought yours."

Paired? That hasn't happened in decades! But—even if that were true, logically, it made sense. Even before this sudden Pairing, we had moments of acting in unison or even speaking simultaneously.

All signs pointed to Pairing. The colors of magic joining, the feeling of being whole, even if before, nothing felt like it was missing. The sudden warmth at feeling it all?

We are two of a Paired Fae.

And it makes sense beyond my fear of the idea. My fear had abated after seeing our magic still twining together like the sprites would during the New Moon balls back in the Summer Court, colors lighting the sky in a dazzling display.

"We will have to discuss this later, my dear fellow, because now, I must see if we can repair the error of my blunder," Holmes said as I followed him into the trap.

"And perhaps this Pairing can be of aid to us!" I called as Holmes snapped the reins, and we drove headlong after where we'd heard the panicked screams before.

And by the Elements, I hope that we are not too late!

And that's it for this chapter. Next time in this AU, we learn more about Pairing, Holmes's life in the Winter Court before he Crossed Over, and diving deeper into how this strange world works.

References this time include: 'The Adventure of the Solitary Cyclist,' 'A Case of Identity,' 'The Adventure of the Copper Beeches,' 'The Adventure of the Speckled Band,' 'His Last Bow,' 'A Tale of Rituals and Fairies,' 'The Sign of Four,' and 'Of Summer and Winter.'

Next time? A classic tale, and feelings are revealed.

Cheers,
Blue