Cas touches Sam's naked skin, just with his fingertips, his caress light and pure as angel's feathers. His eyes are focused on Sam's body, breath from his parted lips warm, but Sam still shivers. He can't help but tense, knowing exactly what patter Castiel's fingers are tracing.
Scars.
Some of them still visible and pink, too fresh and too deep for him to pretend that they're not here. Some of them fading, so pale that if you don't know that they exist, you wouldn't be able to see them.
And some of them are only in Castiel's memory. They vanished after Sam was resurrected with brand new body (brand new skin waiting for new damage torture pain).
But Cas still sees them. But Sam still feels them. They are burned in his soul forever.
Sam's lips are salt with tears when Cas kisses him, trying to ground him to reality, remind him that he's here, with Castiel, not in the past with whoever is hurting him.
"Be my scar, Cas." Sam begs quietly.
Cas puts the hand on his lover chest, where under ribs (broken too many times) his heart is pulsing frantically. Showing that he has survived. Castiel could pray to this heart, grateful for letting him have another day with Sam.
"I am, Sam. I am your scar. Don't you feel it?"
Sam sighs, relaxing under Castiel's warmth spreading through his skin.
Sam's body has too many scars to count.
But his the most important and beautiful scar is on his heart, it has shape of Castiel's name.
They know that it'll never disappear.