Funny enough I remember making what if scenarios of this in my head personally I see it Josuke if he saw Kira 8's killer Queen along with koichi and others would definitely be caught off guard in considering how JoJo's Universe works with the weirdest things happening he probably would assume that this is some sort of reincarnate or resurrection of Kira yoshikage somehow breaking out of hell obviously Kira 8 would definitely be confused and both would absolutely fight each other with Josuke getting the upper hand and strength and raw power however unlike the yoshikage Josuke fought this Kira is far more intelligent with his killer Queen and has far better combat experience then Kira 4 so it's a toss for me on who wins and unfortunately considering out SBR /. Jojolion characters are when it comes to committing genocide I wouldn't be surprised if Kira 8 ended up taking Josukes life however I'm pretty sure something would just stop the two from fighting or there would be some intervention or one of them would just stop the fight in general but other than that there's not much to go off with interactions since Kira a is next to nothing p4's who is a serial killer and josuke would be uneased being around someone like him but eventually would get used to it overtime (also there could be the possibility of Kira definitely confusing josuke for Josifumi for obvious reasons but hopefully they would overcome they're fate)