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
The murderer Anjuro Katagiri targets Josuke with his new Stand Aqua Necklace for foiling a robbery. After Anjuro murders Josuke's grandfather Ryohei, a police officer, Josuke pledges to assume his place as Morioh's protector.

The Nijimura Brothers
Josuke and Koichi Hirose find a dilapidated house when Koichi is struck by the Arrow, soon releasing his dormant Stand Echoes.

The culprits, Okuyasu and Keicho Nijimura, reveal that their father, formerly Dio's henchman, was transformed into an undying, disabled creature 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 prove to them that their father is at least partially human, dissuading them from their activities.

This group is then attacked by the Stand Red Hot Chili Pepper, which kills Keicho and takes the Bow and Arrow. Thus, Okuyasu joins the allies in locating this second murderer.

Koichi Hirose (Echoes)
Koichi is extorted by Tamami Kobayashi of the new Stand The Lock, drawing in Koichi's mother and sister, and provoking the metamorphosis of his Stand into Echoes Act 1.

Toshikazu Hazamada (Surface)
Fellow student Toshikazu Hazamada targets Josuke with his new Stand Surface, assuming his appearance; also attacking Koichi, Tamami and Jotaro.

Yukako Yamagishi Is in Love
When defeated, Toshikazu expresses to Jotaro and Josuke the observation that, as though by fate, "Stand users are bound to meet".

Koichi is kidnapped by classmate Yukako Yamagishi, determined to make him love her whilst holding him with her new Stand Love Deluxe. Koichi's Stand develops again into Echoes Act 2 before he defeats and then rescues Yukako.

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

Red Hot Chili Pepper
After Joseph Joestar arrives in Morioh, the allies are able to defeat Keicho's killer Akira Otoishi, user of Red Hot Chili Pepper. The Bow and Arrow are 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 and Toshikazu meet eccentric manga author Rohan Kishibe, user of the new Stand Heaven's Door.

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

Rohan Kishibe's Adventure
Rohan draws Koichi into helping with his research. The pair discover a ghostly alley inhabited by Reimi Sugimoto; victim of an unknown serial murderer over a decade prior. She begs Koichi and Rohan to find her killer, who remains in Morioh 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 new Stand Harvest. Striking a deal together, Josuke and Okuyasu combat him when he betrays them; finally befriending him.

Yoshikage Kira Wants a Quiet Life
Shigechi discovers Kira's secret and is killed after their confrontation by Kira's Stand, Killer Queen.

People of Morioh
Thus, 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 integrity of her desire for Koichi.

Sheer Heart Attack
With Kira's lost coat button, Jotaro and Koichi track him to a shoe shop, where he attacks with his Stand's secondary power, "Sheer Heart Attack". Koichi's Stand develops finally into Echoes Act 3, and after a battle also involving Josuke and Okuyasu, Kira is able to force Aya Tsuji to alter his features with her Stand, killing her before she may help the group, and escaping.

Atom Heart Father
Jotaro, Josuke, Okuyasu and Koichi investigate Kira's former life and residence. The ghost of Kira's father Yoshihiro Kira appears and attacks the group from a photograph, empowered by the Stand Atom Heart Father.

Yoshihiro escapes with a second Bow and Arrow; aiming to create an army of Stand users in order to protect his hiding son.

Yoshikage Kira's New Face (1)
Kira is shown as having occupied the likeness, home and family of Kosaku Kawajiri. Formerly underwhelmed, Kosaku's wife Shinobu is impressed when Kira steals their monthly rent directly from their visiting landlord.

Janken Boy Is Coming
Rohan is challenged in a series of games of rock-paper-scissors by Ken Oyanagi, user of the new Stand Boy II Man.

Yoshikage Kira's New Face (2)
Kira labors to adapt to his new life while repressing his murderous urges; provoking the suspicion of Kosaku's spying son, Hayato.

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.

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.

Then, Rohan and Josuke swap a motorcycle in battling Highway Star; operated from a great distance by new user Yuya Fungami.

The Cat Likes Yoshikage Kira
Shinobu Kawajiri kills the cat Gatta. Kira finds it resurrected as the Stand Stray Cat, and after a fight, he gives it a home in the household attic.

The Man on the Tower
Josuke, Okuyasu and Mikitaka combat Toyohiro Kanedaichi, user of the Stand Superfly, bound to a transmission tower on Morioh's coast.

Enigma Boy
Josuke and Yuya are confronted by Terunosuke Miyamoto, new user of the Stand Enigma; able to trap opponents in paper once they demonstrate fear.

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, before Koichi attempts to help remove the independent new Stand Cheap Trick from Rohan's back.

Another One Bites the Dust
Kira, desperate at having failed to retrieve Hayato's tape, is pierced by the Arrow; affording him the powerful new ability "Bites the Dust"; a tactic with which, when discovered, he is able to reset time for one day.

The Invincible Crazy Diamond
In spite of 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

 * Let Me Remind You; Town Guardian Spirits; Goodbye, Morioh Cho - The Golden Heart

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 & Mushikuidenai - 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

Yoshikage Kira 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. Yoshikage Kira - 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.