Do you think you'll ever do something where jaskier shrinks?
I've thought about it and how it would work. It'd be pretty different from my usual stuff because Geralt's such a badass, but that wouldn't be a bad thing.
Because even though Jaskier would be a wee little thing, Geralt would just...always know where he was. Always. Bitty bard trapped in the walls after fleeing a rat or some such? He'd be able to sniff and sound him out in seconds and punch right through the wall to rescue him. Tiny troubadour falls out of his personal saddlebag while Geralt's off on a hunt because something startles Roach? As soon as he's done he'd track him through whatever terrain he happened to get lost in. Witchers are insane.
And Geralt is already stronger than average people so he's used to dialing it back; he'd never hold Jaskier roughly--or at least not so rough as to actually hurt him. He could pin him down and make him feel so good with just the tips of his fingers because he's found that a worn out bard gets into less trouble.
Hell, give Jaskier a bit of indestructibility and we can see how far he'd really go to get that bit of pleasure...and what lengths Geralt would go to to keep him contained. If he didn't have to worry about actually hurting the bard he'd be a bit more unrestrained with him. Not the point of cruelty, I can't write that, but doing things just to annoy and piss Jaskier off even if he would still be able to hear the pointed sing-shouting from his boots or his pants.