This was the product of a normally extremely happy person melancholy and a thunderstorm last night. Enjoy! And I, unfortunately, do not own Sherlock, just the plot!
Thunder boomed, jolting John out of his sleep. What was that? he wondered, thinking it was Sherlock. He stumbled out of bed, grabbing his robe on his way out the door. There was another loud crash and John jumped.
"Christ," he muttered. "It's too early for this." He made it down the stairs to find all the lights off and a figure in the window. John rubbed his eyes, frowning. If it wasn't Sherlock, what was it?
"Thunderstorm, John," spoke the figure in the window. "Isn't it silly how people are afraid of them?"
John sighed, shaking his head a little and smiled. "Why are they silly, Sherlock?" he asked, coming to stand next to his flatmate, best friend, and partner.
Sherlock smiled slightly as heard John come closer. "Thunder is hot and cold air colliding violently in the sky. Air causes the huge boom that people are afraid of, the stuff they need to breathe! Isn't it funny, people being afraid of what they need to live?"
"Never thought of it that way," John said mildly, standing next to Sherlock at the window.
Sherlock snorted. "Of course you haven't. Nobody uses their brains, John. They don't think."
John chuckled. "Well, we can't all be as smart as you, Sherlock."
Sherlock looked sideways at John. "You've come the closest."
John raised his eyebrows in surprise. "Me? What about The Woman, or Moriarty?"
"They were born with it, like me" Sherlock dismissed. "But, you. You try to see the world like me, and you succeed, sometimes. No one has ever done that. Especially for me," he finished quietly.
John was quiet for a moment before turning to face Sherlock. "Sherlock." He turned and met John's eyes steadily. "You are the single most brilliant person I've ever met. Everyone else doesn't matter. I love you and you love me and that's that," John said firmly.
Sherlock smiled softly. "I know." He leaned down, closer to John's height. "I love you."
Joh started. That was only the second time Sherlock had said those three words. The first was when they admitted their feelings to one another. Since then, John always started it and Sherlock replied either "I know", or "And I you". John smiled and rose to his tip toes, stretching his arms around Sherlock's neck. "I love you too."
They kissed gently, softly, in the window just as a lightening strike came down and illuminated the room, with the rain pouring down and the thunder booming overhead.