Spoilers for Crazy Diamond's Demonic Heartbreak Ch. 9 ahead.
The Jojo's Bizarre Adventure spinoff series has played its villain's schemes close to the chest, but it seems Crazy Diamond's Demonic Heartbreak is finally ready to reveal who, if not how or why.
The spinoff, which uses characters from both the third part (Stardust Crusaders) and fourth (Diamond is Unbreakable), began with Hol Horse being tasked with tracking down one of DIO's Stand-using pet birds, a parrot by the name of Petsounds. The bird had been stolen and taken to Morioh in Japan, which led to Hol Horse meeting Josuke Higashikata and the pair working together to stop the bird's disturbing stand, which forces people to relive and reenact events it witnessed. However, while they did take down one crossbow-wielding person working in conjunction with the parrot, this man turned out to be a mere underling.
In Crazy Diamond's Demonic Heartbreak #9 they take the captured man to Josuke's police officer grandfather and have him arrested. Afterward, the man is shown in jail sweating profusely and looking nervous, which then transitions into a flashback. One of Grandpa Higashikata's colleagues, Kazuki Karaiya, is speaking to and threatening the man while he's in the back of a police car. But rather than the type of taunts one might expect a cop to make, Karaiya berates him for being useless and attempts to extract information, using Petsounds' incredibly horrific and powerful stand to force the criminal to relive some undoubtedly horrible events. The chapters ends with the man screaming in his cell, still tormented by whatever images he was shown.
Karaiya has appeared before at the police station (and presumably was the shadowed figure giving orders in other chapters), but while he was a bit suspicious, there was no reason to immediately assume he was responsible for any of these events. Since Hol Horse was forced to shoot Petsounds after Jojo's Bizarre Adventures' crossbow incident, the flashback must take place during a previous arrest, before that occurred. That means that everything Petsounds has caused to happen so far--the police inspector who drove through the crowds, the women with knives who assaulted Hol Horse, etc.-- was under Karaiya's orders. But why and how did Karaiya steal DIO's parrot from Egypt, and why would he even know of Petsounds' Stand ability in the first place? The man must have had some kind of connection to DIO, like Okuyasu's father, and likely has a Stand of his own. The Stand Arrow was already in Morioh at this point, after all.
Making the villain of Crazy Diamond's Demonic Heartbreak a corrupt cop certainly makes for an interesting contrast with Diamond is Unbreakable's main villain, the serial killer Yoshikage Kira. While Morioh might look peaceful from the outside, the town has clearly had a lot of problems for a while, something that only became worse when Stand users began to proliferate. Answering one question has only raised many more, however, so it seems insight into Karaiya's goals will have to wait for another chapter of this Jojo's Bizarre Adventure spinoff.