A/N Welcome to my headcanon. I hope you enjoy your stay.
Dean Winchester had been to Hell and back. Literally. His body came back without a blemish- no freckles, no scars, no birthmarks. His skin was baby soft and a light tan color all over, except for his left shoulder. His shoulder was a burnt shiny red. 'Well, he was in Hell. It's incredible he's not one huge burn,' you might say. But Hell burns cold, and this was a mark born of heat. And a mark it was. A handprint now graced his shoulder, wrapping possessive fingers around his flesh. When he first met Castiel, Angel of the Lord, he couldn't keep his eyes from flickering to his large hands, wondering if one of them would fit, cover him completely. He wanted to ask, desperately needed to know. But he knew other things were more important. So he waited.
The first time he tried to ask, Castiel was taken from him. Dean had just begun to stutter out his question when the angel disappeared. Dean was angry, frustrated, but mostly, sad. Cas returned a few days later with an apology. He had been forcibly removed to Heaven for a brief reeducation. He didn't go into details, but Dean couldn't fault him for leaving. Cas tried to inquire as to what Dean had wanted to ask, but the man wouldn't let him, saying it wasn't important and they would talk about it later.
"If it is unimportant, then why will it warrant conversation later?" Dean didn't respond to the angel's question- he didn't have an answer.
The next few times Dean wanted to ask, he chickened out, telling himself Cas looked too stressed, or too tired. He avoided the question for years, until it burst forth with no thought. Dean had meant to ask if a stake would kill the god they were hunting. What instead leapt from his lips was
"What the Hell is it, Cas?" Cas raised a single eyebrow slightly.
"I have already told you, Dean. She is a pagan-"
"Not... not that. What the Hell is this?"Dean shrugged off his jacket and overshirt, then shoved his sleeve over his shoulder, baring the mark.
"You do not know?" Dean scowled.
"If I knew I wouldn't ask." Cas took off his trench coat, laying it carefully over the back of a chair.
"When I raised you from perdition," Cas lay his suit jacket over the coat. "my grace seared your soul. Had you had a body, it would have been burned completely." As he spoke, Cas began unbuttoning his shirt while Dean shifted his weight nervously. What was Cas doing? "But when I gripped you tight," Cas finally removed his shirt. "you gripped me in return," Dean's eyes glued themselves to the angel's arm. Wrapped around his right bicep were two handprints Dean knew would match his own, shaking hands, "and your soul seared my grace." The human brushed the raided scar with a single trembling finger. "As I marked you," Cas nodded to the other man's shoulder, "so you marked me, Dean Winchester."
End