Diamond is Unbreakable

Diamond Is Unbreakable (ダイヤモンドは砕けない) is the fourth part of JoJo's Bizarre Adventure, published in Weekly Shonen Jump between 1992 and 1996.

In 1999, the Arrow, manifesting latent Stand abilities, travels throughout Morioh, Japan; as high schooler Josuke Higashikata (illegitimate son of Joseph) and friends seek out the culprits of a series of homicides.

Jotaro Kujo! Meets Josuke Higashikata
An older Jotaro Kujo travels to coastal Morioh, Japan, in order to meet high school freshman Josuke Higashikata and link him with the inheritance of Joseph Joestar; his aging, absent father. Once Josuke displays his Stand, Crazy Diamond, Jotaro shares the news of a paranormal threat in Morioh; revealed to be the result of the arrival of the Bow and Arrow, an ancient artifact inciting Stand development in suitable individuals, as delivered by one of Dio's henchmen.

Josuke Higashikata! Meets Anjuro
One of the Arrow's targets, the criminal Anjuro, uses his new Stand Aqua Necklace to exact revenge on Josuke's grandfather Ryohei, a police officer, for putting him in prison. Angelo succeeds in murdering Ryohei before he is defeated by Josuke; upon which Josuke pledges to defend Morioh against the potential threat posed by the Arrow's presence.

The Nijimura Brothers
Josuke and Koichi Hirose find a dilapidated house when Koichi is struck by the Arrow, unleashing his Stand, Echoes. The culprits, Okuyasu and Keicho Nijimura, reveal that their father, formerly Dio's henchman, was disfigured and disabled by Dio's cells upon his death, and that Keicho aims to create Stand users in the hope that one of them will be able to kill him. Josuke manages to proves to them that their father is at least partially human, dissuading them from their activities.

Koichi Hirose (Echoes)
Koichi is extorted by Tamami Kobayashi; when he develops his Stand Echoes ACT 1.

Toshikazu Hazamada (Surface)
Toshikazu Hazamada opportunistically targets Josuke. When defeated, he expresses to Jotaro and Josuke the observation that, as though by fate, "Stand users are bound to meet".

Yukako Yamagishi Is in Love
Koichi takes priority when he is kidnapped by psychopathic classmate Yukako Yamagishi, determined to make him love her. Escaping, his Stand evolves into a stronger form. Yukako, impressed, decides to pursue Koichi in a more consensual though no less determined manner.

Let's Go Out for Italian
Josuke and Okuyasu discover the benevolent culinary master Tonio Trussardi; a natural Stand user operating a fine Italian restaurant.

Red Hot Chili Pepper
The group is finally attacked by the Stand Red Hot Chili Pepper, which kills Keicho, and takes the Bow and Arrow. Thus, Okuyasu joins Josuke, Jotaro and Koichi in locating this second murderer. After Joseph Joestar arrives in Morioh, they are finally able to defeat user Akira Otoishi. The Bow and Arrow are then taken into Speedwagon's custody, fostering a temporary peace.

Picked Up Something Bad!
Josuke and Joseph discover Shizuka; an invisible baby (of the Stand Achtung Baby) apparently abandoned on the streets of Morioh; whom Joseph subsequently adopts.

Let's Go Play at the Mangaka's House
Koichi meets manga author Rohan Kishibe, a target of the Arrow, and user of the Stand Heaven's Door.

Let's Go Hunting!
Jotaro enlists Josuke's help in hunting two rats wielding the new Stand Ratt; Mushikui and Mushikuidenai.

Rohan Kishibe's Adventure
Rohan ropes Koichi into helping with his research, when they discover a ghostly alley inhabited by the victim of an unknown serial murderer, Reimi Sugimoto, who died over a decade prior.

She begs Koichi and Rohan to find her killer, who has stayed in Morioh and is still preying on innocent people.

Yoshikage Kira is introduced, speaking as though on a date to the severed hand of a woman.

Shigechi's Harvest
Shigekiyo Yangu appears having collected a minor fortune of loose coins with his Stand Harvest. Striking a deal together, Josuke and Okuyasu combat him when he betrays them; eventually befriending him.

Yoshikage Kira Wants a Quiet Life
When Josuke's new friend Shigechi discovers Kira's secret and is killed, the allies of the story congregate and agree to collaborate in locating Kira and ending his depredations.

Yukako Yamagishi's Vision of Cinderella
Yukako meets Aya Tsuji, the beautician and manager of the Cinderella salon; who trials her with her Stand Cinderella as to the quality of her desire for Koichi.

Sheer Heart Attack
Jotaro and Koichi eventually find Kira, but before he is completely defeated he is able to force Aya Tsuji, user of the Stand Cinderella, to alter his features; killing her before she may inform the group as to his new appearance.

Atom Heart Father
Shortly thereafter, the ghost of Kira's father deploys a second Stand-creating Bow and Arrow to create an army of Stand users to protect his hiding son, in the buildup to the confrontation between Josuke's allies and Yoshikaga Kira.

Yoshikage Kira's New Face
Kira is shown as having occupied the likeness, home and family of Kosaku Kawajiri. Though able to please his wife Shinobu, he provokes the suspicion of Kosaku's son, Hayato.

Janken Boy Is Coming
Rohan is challenged by Ken Oyanagi, new user of the Stand Boy II Man.

I Am an Alien
Josuke and Okuyasu meet Mikitaka Hazekura, who claims to be a 216-year-old extraterrestrial; user of the Stand-like power Earth, Wind, and Fire, which Josuke exploits in cheating money from Rohan in a game of dice (before Rohan's house is accidentally destroyed by fire).

Highway Star
Rohan spots what appears to be a room in a tunnel in which a man bends over and severs the hand of an unconscious woman; before he and Josuke battle Highway Star; operated from a great distance by new user Yuya Fungami.

The Cat Likes Yoshikage Kira
Shinobu Kawajiri kills the cat Gatta, before Kira discovers its new, resurrected Stand, Stray Cat; which finds a home in the household attic.

The Man on the Tower
Josuke, Okuyasu and Mikitaka discover Toyohiro, user of the Stand Superfly, bound to a transmission tower on Morioh's coast; entering it as a trap.

Enigma Boy
Josuke and Yuya are confronted by Terunosuke Miyamoto, new user of the Stand Enigma, who already having trapped Koichi succeeds in trapping Josuke's mother Tomoko.

My Dad Is Not My Dad
Hayato films Kira murdering a man and a woman; beginning a battle to protect this evidence.

Cheap Trick
Rohan is confronted by Masazo Kinoto; as Koichi attempts to help him remove the independent new Stand Cheap Trick from his back.

Another One Bites the Dust
Kira, in desperation, is pierced by the Arrow; affording him a powerful new ability, "Bites the Dust"; a tactic with which, if discovered, he is able to reset time for one day.

The Invincible Crazy Diamond
Despite this, Josuke is able to maintain a battle with Kira, who by now also employs Stray Cat in generating fast, explosive projectile bubbles.

Final chapters
Kira is confronted by the majority of the allies of the story; as Reimi Sugimoto finds peace, and Josuke sees off Jotaro and Joseph.

Major Battles
Josuke Higashikata vs. Jotaro Kujo

- Jotaro Kujo! Meets Josuke Higashikata

Josuke Higashikata vs. Anjuro Katagiri

- Josuke Higashikata! Meets Anjuro

Josuke Higashikata vs. Okuyasu Nijimura

- The Nijimura Brothers

Josuke Higashikata vs. Keicho Nijimura

- The Nijimura Brothers

Koichi Hirose vs. Tamami Kobayashi

- Koichi Hirose (Echoes)

Josuke Higashikata & Koichi Hirose vs. Toshikazu Hazamada

- Toshikazu Hazamada (Surface)

Koichi Hirose vs. Yukako Yamagishi

- Yukako Yamagishi Is in Love

Okuyasu Nijimura vs. Red Hot Chili Pepper

- Red Hot Chili Pepper

Josuke Higashikata vs. Akira Otoishi

- Red Hot Chili Pepper

Koichi Hirose vs. Rohan Kishibe

- Let's Go Play at the Mangaka's House

Josuke Higashikata vs. Rohan Kishibe

- Let's Go Play at the Mangaka's House

Josuke Higashikata & Jotaro Kujo vs. Mushikui

- Let's Go Hunting!

Josuke Higashikata & Okuyasu Nijimura vs. Shigekiyo Yangu

- Shigechi's Harvest

Shigekiyo Yangu vs. Yoshikage Kira

- Yoshikage Kira Wants a Quiet Life

Jotaro Kujo vs. Sheer Heart Attack

- Sheer Heart Attack

Koichi Hirose vs. Sheer Heart Attack

- Sheer Heart Attack

Josuke Higashikata & Jotaro Kujo vs. Yoshihiro Kira

- Atom Heart Father

Rohan Kishibe vs. Ken Oyanagi

- Janken Boy Is Coming

Rohan Kishibe vs. Highway Star

- Highway Star

Josuke Higashikata vs. Highway Star

- Highway Star

Kosaku vs. Stray Cat

- The Cat Likes Yoshikage Kira

Josuke Higashikata, Okuyasu Nijimura & Mikitaka Hazekura vs. Toyohiro Kanedaichi

- The Man on the Tower

Josuke Higashikata & Yuya Fungami vs. Terunosuke Miyamoto

- Enigma Boy

Rohan Kishibe vs. Cheap Trick

- Cheap Trick

Josuke Higashikata, Okuyasu Nijimura & Hayato Kawajiri vs. Kosaku

- Another One Bites the Dust; The Invincible Crazy Diamond

Trivia

 * Araki mentions that some of the enemy concepts in Part IV were leftovers he was unable to include in Part III.
 * According to Araki, the broad plot of Part IV was inspired by real murders occurring in Japan at the time.
 * This arc is notable for taking place both in Japan and in a fictional setting, without travelling to any real locations. The plot is mystery-oriented, not travel-oriented, as characters balance everyday life with encounters with new Stand users and the search for Kira.
 * Exhausting the Tarot and Egyptian mythology in Part III, Part IV primarily references popular (rock) music in its names.
 * For its inventiveness and artwork it occupies a high rank among fans.
 * Araki states that it is possible that JoJo's Bizarre Adventure could have ended with Part III, since the resurrection of Dio was the last plot element of precedent.
 * Sometimes when a character is defeated the character will "shrink" from being around Josuke's height as a villain to Koichi's height as an ally (i.e. Tamami Kobayashi, and Toshikazu Hazamada).
 * Among the community commonly accessing scanlations, Part IV is infamous for the "Duwang translations"; the only scanlations available until recently. A project by two Chinese students who were assigned to translate something into English, they failed their assignment due to how poor the translation is. Its many errors include original names for characters (e.g. Shigekiyo Yangu as "Fatty", and the setting Morioh as "Duwang") and lines like "What a beautiful Duwang" and "Get a feeling so complicated".
 * The title of this arc was formerly translated as Diamond Is Not Crash.
 * Part IV is the only part where three JoJos are present (not counting flashbacks), making it, to date, the part to depict the most JoJos together.