When James and Lily first became friends, one of the first things he had to get used to was her tendency to touch. He was always considered the touchy friend because of his tendency to throw his hand around her shoulders or pick her up and spin her around during a party. But really, it was her. Her touches were just smaller, less noticeable, but far more intimate. She'd grab his arm and twist his wrist to get a look at his watch and his heart would stutter. She'd use his shoulder as leverage as she readjusted her shoe and he'd instantly go pale. When they'd gotten closer, become real friends, she'd started grabbing his hand in the middle of boring classes, playing with his fingers, sketching doodles with a quill on the back of his hand. He'd watch as she filled his arms full of her loopy signature and detailed doodles of figures and creations. She'd make him play tic-tac-toe along his forearm, sketch snitches and hippogriffs along his fingers. And then she'd pass the quill over to him and let him play connect the dots with her freckles. He used them to draw constellations and flowers, dark ink showing up so more clearly on her skin than his own, so plain and in the open and a visual, tangential reminder that they were friends. That she had let him, asked him, to touch her like that.
Then they'd become more. And the smiley faces and stars began to turn into hearts and x's and o's. Little kisses littered across his skin as a reminder throughout his day that she was his and he was hers. Sirius teased him over it mercilessly but James wore the ink proudly, rolling up his sleeves and casting charms to make the ink last throughout the day.
The first time she told him she loved him she did it through ink. He was holding her on the couch in the Heads common room, one arm holding a Charms textbook open as he read a passage aloud to her, the other dangling in her lap for her to sketch on. She scrawled it across his forearm in loopy, beautiful letters 'I love you'.
He made her charm it so the ink would stay long enough for him and Sirius to figure out a tattoo spell.