There isn’t much, but I’ll share the ones I know with you.
You can find most fics on ao3, in the jonathan/dio (or dio/jonathan) tag, and once in a very long while there’s new stuff. There’s also quality stuff in there that I don’t mention in my favorites so you should really check the tag.
also, alovelyburn’s fics - under the Jojo section- ARE REALLY GOOD but aren’t very shippy. I recommend reading them anyway because they are excellent pieces of writing. I also recommend reading her Dio meta that’s both very well thought-out and very well written.
My personal favorites- I’m not so good at giving summaries or talking about what I liked but I can very well try.
E.V.O.L. a few drabbles on jonathan and dio (THAT IN MY OPINION HAS REALLY GOOD CHARACTERIZATION aaaaahhhh)
Okay, I can't help but see imayoshi with a cute, naive kouhai for a s/o? Like they're so sweet and gentle and then their boyfriend is this ruthless cunning basket ball player who is completely whipped by her
Nyaaa it’s a really cute pairing uwu they probably started going out because his s.o somehow obtained the courage to confess to him first - and Imayoshi probably never thought that he’d ever fall for that type of person in a million years, but he was curious as to why someone so naive and innocent would be interested in him so he goes out with them for his own amusement, already planning how to break up with them as soon as he gets bored
But like not even two weeks into their relationship and Imayoshi finds himself more and more entranced by this naive kouhai - they like to cook and for the life of him he can’t figure out why he gets so pissed off when he sees them bringing in bentos for people other than him ??
He starts taking initiative to spend more and more time with them (whereas before it was always his s.o asking if he had anyway free time) and he ends up inviting them to watch one of his basketball games a week or so later - she cleans his glasses for him on her boob before the game and he knows that he’s whipped when he doesn’t even try to look down her shirt