"Are you sleeping?"
"John, can I ask something?"
"Do you wear that all the time?"
John frowned and opened his eyes. Sherlock's face was close to his, eyes glued to his bare chest with a curious, observing look.
It was late at night, but the full moon was luminous enough to enlighten the room. Before he turned his head, John stuck for a moment, seeing a picture of a half-naked Sherlock in this silvery halo. It almost hurt to look away.
But he did, eventually, and followed the other man's stare to his dog-tag, which rested on his chest.
"Ah, this. Yes. I don't even remember the last time I took it off."
"Well, obviously, it's a prescription in the army."
"But you're not in the army anymore."
"True, but it became natural for me to wear it, I guess. Like a part of me, a limb or something like that."
"A limb? John, it's a dog-tag."
"Yes, but" John sat up, absolutely awake now, struggling to find the appropriate words. "In the army, this is your identity, everything that's vital about you. Not merely the name, ID number and blood type, but a symbol… Hell, I don't know how to explain it to you. Let's say it somehow defines who I am."
"A piece of metal as self-definition?"
"You're not a fan of metaphors, are you? I admit it's not perfectly accurate…" John stared down at his dog-tag. "But I have an idea how to add the missing part. Sit up."
"What? Why?" Sherlock groaned, but his body obeyed instinctively.
John looked in his eyes with an expression that made Sherlock's breath stuck in his lungs. He slowly lifted the dog-tag from his neck. Sherlock's brain roared up as it took in every single movement, every screenshot of John, who seemed to glow with gentle moonlight.
John turned the dog-tag in his hands and placed it on Sherlock's neck. He brushed his hair as he pulled the string over his head and Sherlock felt shivers run down his spine. John set the label on his chest, resting his warm palm on it for long seconds. Sherlock's heartbeat thundered so loudly, he could hardly hear anything else.
"Now it's a perfect definition." John said, his voice low and full of affection.
Sherlock exhaled a breath he didn't realize he was holding. He tore his eyes from John and took a look at the dog-tag. He touched it with hands shaking from who-knows-what. The faint light made 'John Watson' flicker on the label. Sherlock wanted to say something, but even his most beloved word (John) was lost in the lump of his throat.
His expression must have been bewildered, because he heard John chuckle.
"You get it now, don't you."
"Yeah." Sherlock whispered. He felt strangely out of breath.
"It looks good on y-" The last word came out muffled as John found himself suddenly surrounded by Sherlock's arms, his head pushed into the pale skin of his shoulder.
"Would you wear it, then?" He asked sheepishly from the black curls tickling his face.
"I'll never take it off." He heard Sherlock's low whisper echoing through his own chest. John blushed.
Later on that night, while listening to John's even breathing at his side, Sherlock didn't sleep. His fingers played with the label as he read the short lines over and over again.' A part of me, a limb or something like that.' Sherlock smiled. A heart.