This owes its existence to
copperbadge 's longfic "Cartographer's Craft," in which a sixteen-year-old version of Sirius Black emerges from the Marauders' Map and proceeds to, among other things, embark on an affair with Harry.
I tried fitting both Ron and Draco in instead of Sirius, but it wasn't happening.
****
There are three scars on the boy's body. One is jagged, a zigzagged flash of light over one arched eyebrow. Sirius tracs one calloused fingertip over it, and Harry winces.
"Sorry."
"No - it's - I don't mind."
The second is also magical - the lines of scar tissue have smooth edges that tell of enchanted origins and enchanted cures. The ornate script - I will not tell lies - is on the palm of Harry's hand. It lies hidden, pressed against the smooth milky skin of Sirius' hip.
The third is long and pink, because the cut was deep. It runs along the inside of Harry's arm, running up Sirius' waist to his ribs.
He lifts Harry's arm and kisses this last mark gently, because the edges are coarse and there are no signs of stitches.