So... I've been thinking. I saw a few posts describing Jaskier how he learns to fight and that Geralt buys him daggers so he can protect himself. Other posts pictured Jaskier using a bow. And I like all of those ideas!
This thin, elegant, and glamorous sword made for thrusting but also for cutting and blocking the opponent's strikes. In skilled hands is no match for the common man’s sword. Imagine Jaskier in his full Viscount of Lettenhove mode unsheathing his rapier slowly, as a warning. Imagine him engaged in a duel and winning hands down because, yes, he is a bard, and he doesn't fight and hunt monsters, but he knows how to fight humans perfectly.
Just imagine Geralt watching him using his sword, and being turned on because when Jaskier holds his rapier he is suddenly much more confident, cocky and aggressive, in a graceful way.
And-just-imagine them training, Geralt with his long, heavy sword, Jaskier with his thin and light rapier. Imagine Geralt trying to not hurt him, but Jaskier is fast, faster than Geralt would think, and Geralt, even with his witcher senses, doesn't want to hurt him. So Jaskier goes feral, fierce, harsh, because the rapier is his weapon, a sword made for him and his hands of bard. And he doesn't win, because it's hard to win against a witcher, but he makes Geralt kneel, kneel before him, with the rapier sharp point at his neck.
And Geralt has his heartbeat running faster than ever, and he knows it's not because of the combat. So he knocks off the rapier with his own sword and hits Jaskier behind the knees, making him fall.
And Jaskier breaths in, breaths out, and smiles, licking his lips, tasting his own sweat. Then Geralt helps him to get up, and they lock eyes, still break-breathing, still with a fast heartbeat pumping in their chest. And Jaskier, still feral, still fierce, clicks his tongue, pulls Geralt down by the shirt and kisses him, hungrily, lustful.
And Geralt kisses him back, dropping his sword and unbuttoning his doublet. Fast, faster.