English isn't my native language and this is unbeta'd, so there might be some mistakes.

Disclaimer: I own nothing but feels and merch.

Enjoy~

Sherlock has always been curious, ever since he was a little kid. The word 'why' is never far away from a kid's lips; however, Sherlock soon stopped asking questions and waiting for someone else to give him the answers he so burned to have. Instead, he tried finding the answers himself.

It is only natural, therefore, that he has spent his five years as a student of Hogwarts School of Witchcraft and Wizardry trying to unveil all the mysteries the school has to offer.

He is absolutely certain that he knows the school better than any other student. Well, almost anyone. His best friend, John Watson, is almost always by his side when he goes exploring, not caring about getting caught and ending up in detention but being only interested in the game. The few times that his faithful companion is not with him, Sherlock informs him of any new discovery.

Most students find him weird, strange, abnormal. That's because, unlike them, he doesn't simply see; he also observes. And he is open about his observations, often embarrassing them as he lets out all of their secrets. He didn't care about their opinion of him (what do they matter? they're all idiots) and was not offended when someone called him a freak.

But John Watson did. And he stepped up for him.

They have been friends ever since that day, in their very first year, when John defended his honour.

John finds him brilliant, amazing; and he often lets him know verbally. Sherlock is, to this day, astonished. How can John find him so fascinating when John himself is far more fascinating? How can he put up with Sherlock? Why does he put up with Sherlock?

He misses having the shorter boy walking next to him, cautioning him but also drawn to the danger their late-night strolls around the school entail. Sherlock has decided to let his friend have some much-deserved rest tonight; he must be exhausted after that intense Quidditch match.

He isn't interested in any sports at all, of the magical or the Muggle sort, but he is always there to watch when John - now captain of his team - plays.

With his mind so preoccupied with thoughts of a certain sandy-haired boy, Sherlock almost misses the mirror.

His feet carry him to it, excitement surging through his veins, curiosity as to what he has unearthed now rising. There's nothing extraordinary about this mirror, but the best things are those that appear normal when they are anything but. It's clearly an antique and a quite magnificent one. It is as high as the ceiling, with an ornate gold frame, with two clawed feet supporting its weight. There are words carved around the top, words that Sherlock can't make sense of. Erised stra ehru oyt ube cafru oyt on wohsi.

Sherlock grins. Finally, after weeks of having nothing to challenge his brain, he has found a riddle to solve.

His light-coloured eyes leave the inscription when he realises that there is something wrong with the reflection. He sees John behind him. How did he manage to walk up to him so stealthily?

"John -" Sherlock starts and turns around to look at his friend and share his newest discovery with him.

Except John isn't there.

Sherlock blinks. His gaze moves back to the mirror and finds John right there, right next to him this time. The gears of Sherlock's brain are now working hard as he cannot comprehend what is going on.

In a state of great confusion, he watches as John's hand slides into his. He looks at his own real hand but there is no one holding it. There is no one standing by his side. And yet, he can almost feel the weight of John's hand in his.

He looks at the mirror again. John flashes him that smile of his that is brighter than the sun and makes Sherlock's heart flutter in his chest. There is so much love and adoration in the shorter boy's eyes that Sherlock almost can't take it.

Does this mirror show the future?

Sherlock dismisses that thought immediately. No one can predict or foresee the future, much less an inanimate object like a mirror. So, that is unlikely, and Sherlock finds that this conclusion pains him. What wouldn't he give to make what he sees become reality...

Is that it? Does the mirror shows a person what they want more than anything? Does the mirror reveal a person's deepest desire, even if it is impossible to ever happen?

His eyes shift to the words again. Is it an ancient language long forgotten? Think, he tells himself. He has to get to the bottom of this.

And then it hits him. Any and all writing would appear backwards reflected on a mirror. And so, Sherlock reads the inscription from right to left.

I show not your face but your heart's desire.

Sherlock gasps. Here it is, a mirror that shows a person's deepest, strongest desire; and it shows him and John, holding hands, very much in love each other, not caring for anything but one another.

This, he decides, will be the first time he doesn't share his new discovery with the boy he loves. Because he will not be able to get over the ache if John sees something else entirely. Madame Pomfrey cannot heal wounded hearts.