I've had this idea for a while now, and because I think it would be interesting I'm posting it here.

(Nearly) every Stand user and every Hamon user from Jojo's Bizarre Adventure (within canon, so no Rainy Day Dream Away or The World Over Heaven) vs every canon Quirk user from My Hero Academia. The fight takes place in a gargantuan abandoned city, and both sides start 20 kilometres away from each other. Quirk Users can see Stands, and whilst they don't know any of the details of the Heaven plan, they do know that they'll lose if they don't wipe out their foes within 3 weeks.

An important note is that Giorno has regular Gold Experience, Pucci has C-Moon and the Stand Disc for Whitesnake and Valentine has regular D4C. Joseph is his Battle Tendency self with Hermit Purple. Dio is his Phantom Blood self with The World, but is limited to 5 seconds of time stop and cannot ingest the blood of a Joestar as his body is his own, not Johnathan's, so it isn't resisting him.. There are no horses at the beginning, however Giorno is free to create them. This fight also takes place in an alternate dimension, meaning that Jojo's dimension rules don't apply here, so amongst other things, Johnny and Johnathan and Dio, Diego and DiAUgo can freely interact. Hamon also works on normal humans like a concentrated electric shock, because that way it isn't completely useless here.

The two sides are still entirely in character. Whilst they will partner up to take on the other side, they aren't automatically a united front, and their own egos and ideals may interfere with the plans of their groups.

The twist is that the Stand Users are defending, not attacking. Their goal is to fortify a central building in their encampment for 3 weeks. This is because that building is built on top of the perfect location to attain Heaven. If Pucci survives for 3 weeks and is able to attain Heaven, the universe resets and the Jojo characters win. If Pucci is, for whatever reason, unable to attain Heaven, the MHA characters win. And, if either side is wiped out, the other side wins. Pucci cannot manipulate gravity to replicate the conditions for Heaven, he must wait the 3 weeks. All sides have enough food, water and resources to survive for 3 weeks. They also have all gear they would normally use, but nothing more than that. No Quirk drugs or Stand arrows. Giorno also doesn't have the Requiem arrow and Valentine doesn't have Jesus's corpse.

The omitted Stand users are the Green Baby (because Pucci has C-Moon) and Lucy Steel to prevent Valentine from obtaining Love Train. And to prevent Pucci having a crisis of faith.

Diavolo, despite canonically dying, coming back and dying again an infinite amount of times in this exact scenario, is not immortal because Giorno does not have access to Gold Experience Requiem, and as such is not in his death loop. Therefore, even though he is still Diavolo, he can be killed, and he will die if he is.

Will Pucci attain Heaven? What tactics will play out to stop him from doing so? Which phases of the siege will be the most impactful? Who do you think will be the major players? Let's find out!