Kazuki Karaiya (仮頼谷 一樹, Karaiya Kazuki), also known as the Ultimate Singer (アルティメット・シィンガー, Arutimetto Shīngā), is the main antagonist of the spin-off manga Crazy Diamond's Demonic Heartbreak and the light novel Crazy Heartbreakers.
Karaiya is a tall man with an androgynous appearance. He has light-colored hair styled in a bob cut, a mole below his right eye, and flat eyebrows. He wears a typical Japanese police officer uniform in the springtime consisting of a hat with an emblem on the front alongside a coat with a white dress shirt and a dark tie underneath.
Karaiya normally presents himself as calm and serious, but beneath that facade lies a hidden darkness and contempt. Ultimately, he is deranged, sadistic, and an elitist. He manipulates Pet Sounds's Stand to attack innocent civilians, including Josuke Higashikata, the grandson of Karaiya's coworker, Ryohei. He goes as far as attempting to murder Josuke, planning to make it look like a suicide. Karaiya allows criminals like Koji Kiyohara to roam free if it means they can be of assistance to his plans, permitting the man to shoot a kindergartner and others with a crossbow.
Karaiya's primary motivation comes from being the only member of his family to carry the remnants of his grandfather Mogizo Karaiya's ideology, which the latter learned from Kars. They believe the winner should focus on being the one who comes out on top. Despite not being athletic and having average or slightly below average grades in school, Karaiya believes that he is the greatest in the world and that everyone else is beneath him. He has a superiority complex, perceiving other people around him as ignorant imbeciles. Like how Kars became the "Ultimate Thing", Karaiya conceitedly refers to himself as the "Ultimate Singer", frequently humming or singing the tune "Sing, sing, Ultimate Singer ♪" like a drunkard. Before his conversations with his grandfather, Karaiya felt lost. However, after getting Pet Sounds by his side, he feels like he could do anything. Despite his self-proclaimed position as an emperor standing at the absolute pinnacle of the world, he questions why others remain oblivious to his greatness.
Karaiya initially acts friendly when socializing with others such as his coworkers and Boingo, but it is merely an act that he puts on, which is a skill he learned from his grandfather. He was told by Mogizo that within the world there are hidden truths that grant those who uncover them the qualification to rise to the pinnacle of everything. This distorted conviction is deeply ingrained in Karaiya. Although he harbors contempt for those around him, he has mastered the art of effortlessly blending in with his surroundings. He patiently awaits the emergence of the truth, assuming a false identity in the meantime like how his grandfather disguises as a human. His decision to become a police officer was driven by his belief that it would bring him closer to uncovering the elusive truth. His calm demeanor can quickly change to reveal his true nature when he is angry. There are moments when stress overwhelms him, reaching unbearable levels. Witnessing foolish and clueless individuals leading carefree lives fills him with fury and disdain towards every single one of them. Even after his defeat, he claims how he will stand above all humans.
- Main article: Pet Sounds's Stand
After sharing a piece of his earlobe with Pet Sounds, Karaiya's soul mysteriously connects with Pet Sounds, allowing them to share the same Stand. Karaiya is capable of fully wielding it for his own gain. Pet Sounds's Stand is capable of recording events from the past in punched cards and inserting them into someone's body. The victim's body is then forced to reenact the event, essentially parroting what happened.
- Main article: Tohth
Tohth is a comic-book-like Stand whose whimsical story periodically updates itself to predict the close future with 100% accuracy. After incapacitating Ryoko and Boingo, Karaiya takes the book for himself.
When Karaiya was young, his grandfather Mogizo Karaiya advised him not to open his heart to humans because of how shallow they are. Before World War II, Mogizo was at St. Moritz, Switzerland for an intelligence operation, where he experienced something that transcended all of creation. Mogizo never shared the truth with his son since he was already born by the time Mogizo became a vampire, but he decided to tell his grandson since he felt that both of them were similar. Mogizo passed on the ideology he learned from Kars and planned to share a part of his vampire essence to him when he became an adult. However, Mogizo went missing when Karaiya was in elementary school, so Karaiya never received his power.
After growing older, Karaiya started working in Morioh as a police officer in the Budogaoka Police Station. In March 1999, Keicho Nijimura stole Pet Sounds in Cairo, Egypt, and brought the parrot with him to Morioh. At some point, Karaiya retrieves the parrot from Keicho; Hol Horse assumes that he confiscated the bird. Karaiya shares a piece of his body with Pet Sounds, linking their souls together and making them share the same Stand.
Attacking Hol Horse
At the Budogaoka Police Station, Karaiya takes interest when Boingo mentions that he lost a manga. Ryohei asks Karaiya to escort Boingo back to his hotel. Before they leave, Karaiya ominously hopes that Ryohei could get a promotion someday for his hard work and passion.
Later, Karaiya has Pet Sounds use its ability to possess a group of chefs. Watching from an alley, Karaiya witnesses Hol Horse using his Stand to defend himself and is excited to learn that there are other Stand users in Morioh.
Without directly meeting him, Karaiya gives Koji Kiyohara permission to kill whoever he wants, while also having Pet Sounds attack Josuke and Hol Horse. However, Kiyohara and Pet Sounds are both defeated by the duo, allowing Ryohei to arrest Kiyohara. While Kiyohara is in his jail cell, he sees a memory of Karaiya sitting beside him in a police car. Karaiya asks him how it felt to lose. When Kiyohara doesn't answer the question but instead asks who Karaiya is, Karaiya screams at him. Pet Sounds then appears behind Karaiya and activates its Stand ability on Kiyohara, causing him to shriek in his cell.
Karaiya looks at the civilians around him and feels that he is superior to all of them. Recalling his grandfather's words from when he was younger, Karaiya has full faith that he can crush anyone that stands in his way. Karaiya walks up to Boingo, who is taking shelter from the rain, and asks if he needs a hand searching for his book. However, Karaiya actually incapacitates Boingo and carries him with one arm while looking for Tohth. He eventually finds Ryoko Kakyoin and uses Pet Sounds's Stand to possess her. With Tohth left on the ground, Karaiya picks it up and becomes its new owner. The pages tell him to give Ryoko a gun so that she can shoot Hol Horse. Karaiya is ecstatic that he can now control both the past and the future using Pet Sounds and Tohth.
Karaiya then uses Boingo as bait to lure Josuke into a trap. Despite Josuke's caution, he falls for it and Pet Sounds is able to attack him. Josuke and Boingo manage to break free from the illusion thanks to Josuke's Stand, causing Karaiya to grind his teeth in anger wondering what kind of ability Josuke has. He assures that no matter what tricks Josuke uses next, he will never win against the abundant memories Pet Sounds has stocked up. He declares that his next attack will be a massacre and he'll kill all of them.
When Josuke, Boingo, and Hol Horse reunite, Karaiya tricks them by using a paper model of Pet Sounds and an illusion of Ryoko to split them up. Josuke runs after the fake Ryoko, and Hol Horse chases after "Pet Sounds". After Karaiya successfully splits them up and isolates Josuke, he makes Josuke relive a memory of Daniel J. D'Arby playing poker with DIO. While Josuke is defenseless, Karaiya comes behind him with a cutting torch and intends to make Josuke's death look like a suicide. Luckily, Josuke manages to escape the memory by punching Pet Sounds before Karaiya could harm him. Karaiya tries to act innocent, but Josuke sees through his trick and punches him with his Stand.
Karaiya attempts to have Josuke hear The World's Stand cry, which he claims is the most powerful sound. Pet Sounds plays the sound with its Stand and Karaiya boasts about taking his place far above humans and looking down on everyone. Fortunately, Josuke is unharmed and only complains about his ears ringing. He had previously broken Pet Sounds's beak when he punched the parrot earlier to escape the D'Arby illusion. Josuke realized that the secret to Pet Sounds's ability is parroting back the exact noises it hears. Since its beak is broken, the sound it parrots will be off-key, and the ability will be useless. Josuke also figures out that Pet Sounds ate a piece of Karaiya's ear, so he uses his Stand to reattach the piece of Karaiya's ear that was in Pet Sounds's stomach. Josuke remembered Karaiya saying he wants to stand far above humans and look down on them, so he gives him exactly what he asked for. Karaiya becomes a hot air balloon after Josuke's Stand fuses the cutting torch with his skin and fuses his arms with a curtain.
Ryohei and the other officers eventually recover a handgun at the construction site, and also find Karaiya strung up on a nearby tree. Karaiya had taken the gun without permission from a colleague. The upper management of the police force struggle with the decision of whether to treat him as retiring due to mental illness or to dismiss him for violating the code of conduct. They aren't able to interrogate him as he is mentally unfit to answer any of their questions. He is expected to be hospitalized for at least six months, requiring multiple surgical procedures to remove the sheets that Josuke fused to his entire body.