I have no idea where I will be going with this plot-wise (you're free to leave some ideas, if you'd like), but here, enjoy. I don't own One Piece or any of it's characters.
They meet in the middle of a bitter winter, with frost settling between Luffy's joints. Despite the chill, he's still in a pair of worn flip-flops, with the leather thong snug against his toes. He'd go barefoot all the time, if he could, but then he'd risk giving Ace a premature heart attack. Warm air courtesy of his lung heat his knuckles. Exhaled with an almost obnoxious ah and then a childish laugh that matches his face. He's in the city's public library, a backpack with fabric similar to a potato bag slung over his shoulders. School uniform obscured by a large (large as in damn near reaches to his knees) cardigan, threads decorated in a blocky tree print. There's a straw hat bound by twine hanging off his neck.
He doesn't match at all; but that's okay—because it's Luffy.
One of Law's hands is curled around a paper cup filled to the brim with coffee (as black as his soul). It's companion is flipping through a medical textbook at an almost inhuman pace. There's a pair of glasses sliding down his nose, the black frame clashing with his somehow sickly-tan skin. He's dressed more appropriately for the weather: clad in black jeans and a dull gray sweater, with dirtied runners, and a coat slung over the spine of his chair. The bags underneath his eyes tell a tale of nights spent pouring over homework despite the fact that he's had one too many swigs of whiskey. He reeks of cigarettes and his ears are tucked underneath an out-of-place furry hat. He has some ink marks on the back of his hands—winding around his tattoos. Notes, because he ran out of room in his notebook.
How they meet, is a total and utter cliché. Luffy now has a similar cheap paper cup cradled between his hands. God bless the library's little café. Hot chocolate that warms his tongue and soul. Well, actually, it burns the tip of his tongue—he's much too impatient to wait for the drink to cool down. He's here to study, just like Law; Ace and Sabo are simply much too distracting of older brothers for Luffy to actually focus on homework. These tables and chairs are way too close together and Luffy nearly trips more than once as he weaves through them—until he actually does trip, foot caught around the leg of Law's chair. It's not a huge tumble. He loses his hot chocolate and the tops of his feet are scalded with the liquid. Luffy doesn't even notice. He's always had a high pain tolerance.
The fall he takes for Law, though, is much, much deeper.