i.
Wizarding children don't play with toy swords. The sticks they pick up in the garden and chase each other with are pretend wands, always. And wands can kill, yes, but they can also put things back together again, and though they've heard of using them to kill, they've seen their parents peel potatoes and repair windows with them, and they're just part of everyday life. There's no limit to what they can do, in the right hands, with the right motion, with the right words spoken, but they're used for small tasks, too.
(Swords, you know, can only cut.)
ii.
He learns how to play chess from Bill the summer he's seven. He and the twins and Ginny have the chickenpox, and Mum has her hands full with trying to keep all of them soothed and entertained. Bill appears in Ron's doorway with his chess set in hand, and Ron hears Percy sniff as he walks by and mutter something about how it's no use trying to teach little Ronnie to play a game so complicated: They called it the game of kings.
But Bill's an excellent teacher, and there isn't anything Ron wants more at the moment than to impress him and to prove Percy wrong, and maybe it's as much determination as it is skill that helps him master the game. For two weeks he eats, sleeps, and breathes chess; it's all he thinks about, he even forgets the itchiness, and he sleeps with Bill's set under his bed so that he can whip it out in the middle of the night if he wakes up with a particularly excellent move in mind.
(With it that much on his mind, it's to be expected that he'd have dreams of a life-size chessboard.)
iii.
From the moment he walks to the edge of the giant chessboard, he forgets to be scared. He sinks back into that place he first visited that scratchy summer sitting crosslegged on his bed bent over the worn pieces, that place he can only escape to when his vision is filled up with the alternating dark and light squares--the place where insecurities fall away and the need to prove himself is dulled, and it isn't about brothers or being a Gryffindor or Harry or Hermione or rejection or competition. The only thing is the game, the strategy, the weighing of options, deciding what can be sacrificed and what must be protected. He knows what to do, and he doesn't hesitate.
(The fist swings down and before everything goes black, he feels a moment of pure satisfaction.)
iv.
The Sword of Gryffindor comes into his hand, even though Dumbledore left it for Harry. It's heavier by far than a wand, and thicker, and the water-cold pommel is nothing like the skin-smoothed wood. It feels wrong in his hands, and Harry's insisting that he be the one to use it, and all he can think about is those days of wearing the Horcrux around his neck, when things he knew rationally couldn't bear up under the weight of the way he felt.
And hearing every single one of his insecurities spoken right out loud, enacted before his eyes, it's like being turned inside out till everything he keeps inside is right there for anyone to see. If he had a wand in hand at that moment, there's no telling what he'd do with it. But what he has is a sword, and so he slices.
(It's enough.)