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Official Site: Viz Media

is the fourth story arc of the Japanese manga series JoJo's Bizarre Adventure, written and illustrated by Hirohiko Araki. It was serialized in Weekly Shōnen Jump from 1992 to 1995, with the 174 chapters collected into eighteen tankōbon volumes. In its original publication, it was titled JoJo's Bizarre Adventure Part 4: Jōsuke Higashikata. It was preceded by Stardust Crusaders and followed by Golden Wind.

Araki introduced the Bow and Arrow in this arc, which causes characters pierced by it (and strong enough mentally) to develop a Stand ability. This was used on DIO at the beginning of Part 3, which not only gave him a Stand but caused Stands to develop in the Joestar bloodline as well. The arc was adapted into an anime television series by David Production, JoJo's Bizarre Adventure: Diamond Is Unbreakable, that began in April 2016. A live-action film adaptation by Toho and Warner Bros. titled JoJo's Bizarre Adventure: Diamond Is Unbreakable Chapter I was released on August 4, 2017. Viz Media has licensed the manga and started to release it in English on May 7, 2019 in a compiled format.

In 1999, in the town of Morioh located in S-City, M-Prefecture, a freshman named Koichi Hirose meets a man looking for Josuke Higashikata, a popular boy in high school. Josuke, who is the illegitimate child of Joseph Joestar, soon encounters the man, who introduces himself as Jotaro Kujo. Jotaro's arrival in Morioh pulls Josuke into the world of the supernatural powers known as Stands, as he becomes involved in Jotaro's search for the Stand-creating Bow and Arrow; Josuke himself is revealed to possess the Stand Crazy Diamond, which has the ability to return any object or living creature (except himself or any deceased being) to a previous state. Josuke and Koichi eventually come across a pair of Stand-using brothers, Okuyasu and Keicho Nijimura. Keicho is revealed to be the one possessing the Bow to create Stand users, turning Koichi into one. After he and his brother are defeated, Keicho is killed by the Stand Red Hot Chili Pepper, which takes the Bow and Arrow. Okuyasu joins with Josuke's group to avenge his brother, encountering several other Stand users before they eventually find and defeat Akira Otoishi, Red Hot Chili Pepper's user, as Joseph arrives in Morioh. The Bow and Arrow are taken into Jotaro's custody and all seems to be over for the moment.

Soon afterward, after Josuke spends time with Joseph, the group encounters other Stand users such as eccentric manga artist Rohan Kishibe, middle schooler Shigekiyo "Shigechi" Yangu and an aesthetician named Aya Tsuji. Koichi and Kishibe later stumble across the mysterious Ghost Street where they meet the ghosts of Reimi Sugimoto and her dog Arnold, learning that they were murdered a decade ago by a serial killer who is still lurking in Morioh. The culprit is eventually revealed to be a handsome office worker named Yoshikage Kira, who seeks to satisfy his murderous urges while living a peaceful, quiet life. Kira has acquired a Stand named Killer Queen, possessing the ability to turn anything it touches into a bomb. When his act of murdering Shigechi to conceal himself backfires (resulting in a brief battle with Jotaro and Koichi in which he is injured), Kira uses Aya to assume the identity of a man named Kosaku Kawajiri, kills them both, and disappears. Kira's father Yoshihiro uses a second Bow and Arrow to create an army of Stand users to protect his son, including a dying cat that reincarnated as a Stand-plant hybrid named Stray Cat, which shoots bubbles of compressed air at its target.

Koichi Hirose has not been a contender in any CBUB matches.