I realize the chapter is a bit spoilery, but hey you're likely following the story as it's being written. So who cares?

Doppio watched as the group entered the Coliseum. 'Looks like the boss won't have to worry about Cioccolata and Secco destroying Roma. Buccellati's group took care of that for us. The bad news is they got to the Coliseum successfully as a result. But that man's Stand...' He made ringing noises again and grabbed his phone. 'I recognize that man. He and some friends of his dealt me my first true loss. It may be too dangerous to confront them at this point. Try to get close and see what sort of secret he has for them. We might be able to take advantage of it for ourselves.'

"Glad you all could make it here alive," Polnareff said as he led the group to a makeshift base on the upper stands of the Coliseum, "Guess lots of things changed..." "Changed?," Buccellati asked. "From the prime universe," Polnareff explained, "Or something like that. I don't fully understand it myself, but Mister Valentine mentioned how things were going more smoothly for those of us who fight to protect justice in the world. Something to do with alternate realities, I think. But that's not important. What's important is now that we've met, I can explain a lot more about what's going on."

"I'd like to know who you are exactly first," Abbacchio said. "I suppose I can bring you up to speed," Polnareff replied, "My story starts back about twenty years ago. I was just developing my Stand's power, when I heard the terrible news. Another Stand user had raped and murdered my sister. While the police did a search for the culprit, they didn't know about Stand power and thought the criminal was local. I knew better, and sought to bring him to justice."

He got out the arrow he showed them before. "In doing so, I learned that a man named Diavolo had sold off five Egyptian arrowheads. Supposedly they could grant Stand powers. Thinking this could be a lead to the man I sought, I traced the purchase. And that's when I ran into a man named DIO Brando." Giorno's eyes widened, and he got out his wallet with the picture of DIO. "My father..." Polnareff nodded. "For what it's worth, I'm sure he'd have relished the idea of raising a child. But that's neither here nor there."

He put the arrow down. "DIO used his powers to control me, and sent me after the Joestars. However, I was defeated upon meeting them, and Jotaro Kujo, who is the grandson of the current head of the family, released me from DIO's control. When I told them my story they reasoned that the man I sought must work for DIO, so I decided to join them hoping to find my vengeance. In the end I succeeded, but continued with the group to stop DIO before his actions could cause more innocent deaths."

"I guess," Rarity said, "You succeeded in the end." Polnareff nodded. He looked to Giorno, but his expression didn't change. "I never even knew my real father. The only reason I know what he looks like is because of this picture. Mother stopped speaking about him after his death, and just continued on her wild partying lifestyle, before she married my stepfather. So if the Joestars are worried I might seek revenge, they shouldn't be. I've no need to take revenge for someone I never had an emotional attachment to."

Polnareff breathed a sigh of relief. "Jotaro will be grateful to hear that. Especially since he was the one to kill DIO to save his own mother." He motioned for the group to follow him. "But the details can wait. After all, you came here hoping to find the means to overpower Diavolo." "You said you fought him before," Fugo said, "Did your Stand help with that?" "On its own, no," Polnareff replied, "Silver Chariot is fast, but what does that matter when time is getting erased, allowing someone to avoid getting hit at all?"

'Yes, he was with a group that managed to track me down,' Diavolo said over Doppio's phone, 'Working together they overwhelmed me, coming in from a number of angles. Ultimately I was forced to retreat. It's the one loose end I've never been able to tie up, but I never bothered to because up until now I didn't think it would amount to much. By the time they could start looking for me I was already erasing every trace of my identity, and even if they could find me they had Passione to get through.'

"And now he has Buccellati's group with him," Doppio realized. 'For now do not approach. Just blend in with the tourists, and try to get close enough to find out what they came here for. If it's something we can use, we'll steal it. If not, we'll destroy it. But until we have more information, it's not worth the risk to get inside their collective attack range. They were strong enough to take on Cioccolata and Secco, and we have no one else capable of dealing with them. At this point any further attempts to send agents after them is just going to hurt our organization.'

"Then I'll see what I can learn," Doppio said as he got a ticket for the tour and started looking for where the group had gotten too. He finally spotted them and took a careful seat among a crowd of visitors. Meanwhile Polnareff was still talking. "Mister Joestar once told me of several members of a superior race right below us. Only one of them left, though. But I digress. In order for you to understand what it is that makes this arrow special, I should tell you something I learned from Mister Valentine."

"What's that?," Buccellati asked. "The history of Diavolo," Polnareff said, "Now understand that Diavolo was very thorough in erasing all traces of this story, but even he couldn't account for a Stand that can look into alternate realities. And from what Funny Valentine tells me, the history of Diavolo is identical in both this world and the one he peered into." Doppio, who overheard this, was a little surprised. 'If the boss is hearing this... I'll bet he's surprised as all hell.'