In such a world where Jonathon Joestar is still alive, if he is the only Joestar. Did Pucci use his stand in such a way to make the later Joestars never be born?

Well, no.

In fact many Joestars are alive in the present day. How?

Well as one may recall Hamon slows aging and since Jonathon Joestar continued to use Hamon in this world he has aged to around 40 despite being nearly 150 years old.

In the new world, Stand users are arranged into hero agencies, and as a family of powerful stand users, they too work for a hero agency founded by the late Speedwagon, God rest his soul.

So where are they right now? At this moment as Deku enters U.A. academy?

"Yare yare daze," Jotaro sighs adjusting his white hat, "Another bum robbing a gas station? So annoying. Grandpa, you ready?"

"Don't call me grandpa," Jonathon replies, "I'm going to outlive you, you know."

"At least I have a useful Stand," Jotaro retorts, "Your Stand [We Will Rock You] is basically a weaker [You Say Run]."

[We Will Rock You], which takes the form of a gentlemen in a black suit with a red tie, appears behind Jonathan as he retorts, "[We Will Rock You] may not have the oomph of [You Say Run] But it has one thing [You Say Run] will never have."

The criminal has a major headstart of nearly 300 meters, but in the blink of an eye, Jonathan is able to get in front of the criminal as he smirks, "[We Will Rock You] is way faster than [You Say Run]."

With a Zoom Punch, Jonathan stops the thief dead in his tracks before the police arrive on scene to take the criminal away.

"Well I suppose that's a job well done," Jotaro shrugs.

"Reminds me of that time All Might and I fought Dio on that boat all those years ago," Jonathan replies.

"How did that go down anyways?" Jotaro inquires.

"It was over a hundred years ago..." Jonathan replies.

All Might and Jonathan were, in this new world, best friends since childhood. They fought Dio and learned Hamon side by side. As All Might explained, together they fought Dio on that boat and as the boat burned...

"Get up man!" All Might exclaimed lifting the beaten and injured Jonathan onto his back, "I'm not leaving without you!"

All Might rushed through the halls of the burning ship, ashes and smoke clouding his vision as he pushed through flames that seared his skin.

"Save yourself All Might!" Jonathan pleaded, "Your life is more valuable than mine! You have more years ahead of you! You're more youthful!"

"Cut the chivalry!" All Might retorted, "All human life has intrinsic worth and I'm not leaving my best friend behind! You're the better Hamon used by far and someone has to protect the world!"

All Might lept off the ship just in time to escape the explosion, saving them both. From there the two worked for the Speedwagon Foundation as heroes, eventually forming the Shining Star hero agency that they work for in the present day. However for many years the two walked seperate paths, vowing to meet again, so much of All Might's youth past that, such as how All Might acquired [You Say Run] is unknown.

In addition, the events of the boat left All Might revert injured, an injury that the effects of could only be delayed for so long until they begun to take their toil in the present day.

In present day the heroes return to the agency to find Joseph Joestar, who has aged less gracefully due to his neglect of Hamon, reading an old book about the Pillar Men.

"Everything alright gramps?" Jotaro inquires.

"Respect your elders," Jonathan reminds.

"Oh," Joseph replies, "Just thinking about the old days."

Joseph closes the book and continues, "Any word on tracking that serial killer?"

Jotaro shakes his head, "No, we don't even know the name of his Stand but he must be a powerful stand user as he leaves minimal evidence."

"What do we know?" Jonathan inquires.

"Only that his killings are no longer occurring in Morioh," Joseph explains, "Whoever he is he is smart, meticulous, and he could be anywhere. We don't even know what kind of Stand he has."

A teacher at U.A. sets his books on his desk.

"He could change his appearance," Joseph proceeds.

The teacher begins to write his name on the board in front of his class.

"He could be in this room right now," Joseph explains.

The teacher turns to greet the new students of U.A. academy.

"He could be anyone," Joseph explains, "Anywhere. The only thing we know is that he is walking among us. He could even be posing as a hero!"

The teacher turns and greets his class as Deku sits, ready to learn, eager in fact, not knowing that the man who stands before his class, class 1-A, is...

"Hello students," the man greets, "I am hero number 14, Yoshikage Kira. My Stand is [Killer Queen] and I'll be teaching you all today..."