it would definitely be a big relationship milestone.
guts would be the one to ask for it. griffith… hm idk whether he’d be outwardly reluctant, but i think he would definitely be trepidatious, like, i think he’d be irrationally terrified of triggering guts, especially while topping him, even if guts reassures him that even if he freaks out it’s be nbd in the grand scheme of things and they can just try again another time.
i’m assuming that like canon guts has already been triggered during sex at least once and therefore they know it’s a possibility.
so griffith would be super slow and careful and pull out all the stops to make it as good as possible, setting the mood, making out/foreplay beforehand, mb rimming, blowing him while slowly fingering him, etc.
and I think Guts would love that btw, he might roll his eyes and tell Griffith to hurry up but he would be so into being slowly and thoroughly made love to. all griffith’s focus and energy being directed at him. he wouldn’t be v responsive though lol, i could see griffith asking for reassurance 50 times and guts like, ‘yes it’s great, you’re amazing, get on with it’ because I just don’t see guts as all that vocal in bed.
also i like to think that it goes perfectly fine, at least the first time. i don’t think one flashback and pouring his heart out once would actually fix guts’ childhood trauma lol, i’m sure he’ll be triggered more than once in his life, but ptsd flashbacks aren’t exactly super predictable afaik and i mean it would just be nice if guts enjoyed his first time bottoming.
and then afterwards griffith would just be super blown away by guts trusting him enough to ask him to fuck him, and tbh i think it would be a bigger deal to griffith than guts, like it wouldn’t be meaningless or anything to guts, but i think he’d downplay it a bit.
a few years down the line they start occasionally playing rock paper scissors to decide who has to top lol. though overall i think guts would still top more often, less because of trauma and more because i just hc him w/ more verse tendencies than griffith.
ETA and I just noticed you also asked in general not just first time, so I also want to add that I think Griffith wouldn’t be super into topping. He’d be into Guts wanting him, but along w/ my sub Griffith hcs I think that he’d prefer to lay back and experience rather than create the experience for Guts, yk? he’d find topping stressful. otoh I think he would absolutely do it if Guts wanted it and he wouldn’t really think of it like that to himself, he wouldn’t think of topping as something that stresses him out and makes him overthink lol, he’d just put too much effort into it and wouldn’t really be able to relax and enjoy the experience.
Like I can see where top and/or powerbottom Griffith comes from, and I could def see Griffith taking charge during sex (particularly power bottoming, esp when they first get together. Griff on top, riding Guts, controlling the pace and initiating things, etc), I think he’d be p good at it too, but I don’t think he’d prefer it, basically.
hbu, what are your Thoughts?