A detailed chronological summary of the life of Okuyasu Nijimura.
Background
Okuyasu was born in 1983 as the younger brother of Keicho. He lived in Tokyo in the economic bubble era. At one point, their mother passed away and their father's business failed, forcing him to take out heavy loans. The father often beat up Keicho and Okuyasu in frustration. However, he then suddenly received money and even jewels, turning the family's economic situation around.
Suddenly in 1989, their father began to mutate into a monster. DIO had planted a flesh bud in his head that went out of control the moment he died. In one year, their normal father transformed into an abomination. Later, the two would learn that he had been working for DIO in exchange for money. Okuyasu would assist his brother in looking for a way to kill their father and put him out of his misery. The Nijimura brothers use the Bow and Arrow to give themselves Stands, before they begin to use it in order to find a user capable of killing their father. They also move to Morioh.
Diamond is Unbreakable
Battle Against Josuke Higashikata
One day, Josuke Higashikata and Koichi Hirose stumble upon their house. Curious, Koichi looks through the gate only for Okuyasu to violently slam it shut on the trespasser's neck, angering Josuke. At the same time, Keicho shoots Koichi with the Arrow. To stop Josuke from approaching Koichi, Okuyasu reveals his Stand, The Hand. Nonetheless, Crazy Diamond hits him easily. Chastised by Keicho not his stupidity, Okuyasu is distracted and lets Josuke approach Koichi. He rushes to attack, The Hand's palm ready; however, Josuke senses danger coming from the palm and avoids its swipe. The house gate is partially erased, making Josuke understand The Hand's power. Okuyasu decides to teleport Josuke in range, but Josuke ducks, revealing that The Hand also brought flower pots with Josuke. The pots hit Okuyasu in the face, stunning him. When he regains his senses, he runs to the house' entrance, eager to fight, and tries to call off Keicho's Bad Company's attack. Instead, all he does is warn Josuke and get in the way of Bad Company's attack; he is shot in the face multiple times. Josuke is temporarily driven off the house and takes Okuyasu with him.
When Josuke interrogates him about Keicho's Stand, Okuyasu refuses to divulge anything. Surprisingly, Josuke heals him and lets him be on the condition that he doesn't try to attack him again. Astonished, Okuyasu follows Josuke and ask him why he doesn't heal his hand, to which Josuke answers that he can only heal others. Touched somehow, Okuyasu helps him retrieve Koichi, leaving when Josuke is about to fight Keicho.
When the battle settles, and Josuke and Koichi come across their father, Okuyasu attempts to persuade his older brother to stop using the Bow and Arrow to make Stand users. After explaining their story, Keicho is suddenly killed by the Stand Red Hot Chili Pepper, who steals the Bow and Arrow. Okuyasu is saved by Keicho who shoves him out of the way. Seeing his brother's corpse on the power lines, Okuyasu states that he certainly had it coming, but still mourns his sibling who showed he truly cared for Okuyasu. He later befriends Josuke and Koichi, enrolling in their high school, Budogaoka, and ending up in the same class as Yukako Yamagishi.
Koichi Hirose (Echoes)
One day, Okuyasu and Josuke see Koichi being bamboozled by Tamami Kobayashi, a hustler accusing Koichi of having killed his cat and demanding 500,000 yen in compensation. Tamami's Stand, The Lock, automatically sticks itself of a person feeling guilt and multiplies the effect of the guilt. Angry, Okuyasu punches Tamami, who falls face first on the pavement and breaks a tooth. Tamami wails, making Okuyasu feel guilty. The Lock appears on him and Tamami threatens to make him pay for his front tooth. Thankfully, Josuke heals Tamami and reveals that the cat was merely a toy. Shocked by Josuke's power, Tamami flees but takes Koichi's money with him.
Later, Okuyasu and Josuke are shocked to see that Tamami has shrunk and somehow has become Koichi's lackey.
Yukako Yamagishi Falls in Love
One day, Okuyasu and Josuke surprise Koichi having a date with a girl in a café. This girl is Yukako Yamagishi, one of Okuyasu's classmates. The two naturally decide to spy on them, and Okuyasu feels jealous and sympathetic for Koichi's apparent luck. However, Yukako then reveals that she's subject to violent mood swings and Okuyasu doesn't feel that Koichi is lucky anymore.
Later, Okuyasu and Josuke see Koichi's class representative in danger, her hair set on fire and blinded and tongue-tied by Yukako's hair. Thankfully, The Hand scrapes away the burning hair, saving the representative, but leaving a big bald spot on her head.
Later, Okuyasu, Josuke and Koichi try to discuss what to do about Yukako. Koichi's so disturbed he completely failed an English test, even worse than Okuyasu. Josuke proposes that Koichi appears undesirable from this moment and Okuyasu even advises Koichi not to wash his teeth, wear the same underwear every day, breed lices in his hair, fart all the time, drool and sneeze and wear smelly socks. However, Koichi refuses to go to such lengths. They settle on merely slandering him within earshot of Yukako. Okuyasu and Josuke proceed to accuse Koichi of shoplifting when Yukako passes by. Although she doesn't react, they can feel her murderous aura. Unfortunately, their plan backfires when Yukako kidnaps Koichi the same evening.
The next morning, Okuyasu and Josuke try to look for Koichi. Josuke finally receives a call from a payphone that tips them off on the general location of Yukako's hideout. By the time they arrive, Koichi has neutralized Yukako by himself, however.
Trouble in Tonio's Restaurant
One day, on the way home, Okuyasu and Josuke see a sign showing that a new Italian restaurant has happened. Eager to eat something more refined than his cooking, Okuyasu tells Josuke to come with him eat at this restaurant, managed by the Italian chef Tonio Trussardi. Trussardi's restaurant is particular as he diagnozes Okuyasu with fatigue, two cavities, a stiff left shoulder, diarrhea, and athlete's foot. Moreover, Trussardi doesn't have a set menu but decides of what he will serve depending on the client.
Okuyasu tastes the mineral water and is delighted by its taste. This brings him to tears, in fact he cries worrying quantities of water to the point his eyes shrunk. But then Okuyasu feels cured of his sleepiness. Trussardi then brings the appetizers, tomato and mozzarella slices. Okuyasu is unimpressed by the taste of the cheese but when he eats the mozzarella with the tomato as Trussardi advises, he realizes the harmony between the two ingredients and sees how delicious the dish is. Okuyasu is so charmed he refuses to share with Josuke. Okuyasu's shoulder suddenly itches and when he takes off his jacket, he sees that it is releasing an enormous quantity of dirt. Freaked out, Okuyasu then realizes that his stiff shoulder is cured. Okuyasu is completely taken by Trussardi's cuisine.
When the chef brings a plate of spicy spaghetti alla puttanesca, Okuyasu is reluctant to try the dish because he cannot bear spiciness. However, he eventually tries and swallows the whole plate. His jaws then shoot out two bad teeth, only to replace them with a pristine dentition. Suddenly, Okuyasu feels a terrible stomachache. After Josuke goes to the kitchen, Okuyasu follows him and stumbles on the main dish, lamb with applesauce. Eating the dish despite his pain, his guts explode. However, it merely rejects afflicted intestines and cures Okuyasu's diarrhea. The misunderstand is cleared and Trussardi is revealed to be merely a benevolent chef, although with a strange cooking. Okuyasu finishes his dinner with a pudding, which he finds similarly delicious and which cures him of his athlete's foot.
Battle Against Akira Otoishi
One day, Jotaro summons Josuke, Okuyasu and Koichi to an empty field. Okuyasu comes with his motorbike. Asking what is the matter, Okuyasu is told by Josuke that Red Hot Chili Pepper has visited him last night, which gets on Okuyasu's nerves as he reminded of his brother's killer. Jotaro comes and explains that Joseph Joestar will be coming to Morioh and help find the user of Red Hot Chili Pepper. However, Red Hot Chili Pepper appears from Okuyasu's motorbike and has heard everything. It starts the motorbike and proceeds to drive away.
However, Okuyasu summons The Hand and teleports to his motorbike. The Hand swipes, but Red Hot Chili Pepper easily evades the attack, stating that the movement is too slow to catch him. However, Okuyasu was aiming at his own motorbike. The bike crashes, leaving Red Hot Chili Pepper on the ground and isolated from all power sources. Okuyasu tries to interrogate the Stand about its user, but quickly reveals that he wishes Red Hot Chili Pepper to shut up so that he has an excuse to kill him. Okuyasu attacks and though Red Hot Chili Pepper's speed allows it to land solid punches, the teleportation properties of The Hand's powers take it by surprise and Okuyasu is able to violently stomp it into the ground. Red Hot Chili Pepper's energy reserve deplete as the rest of the heroes approach. Red Hot Chili Pepper thus psyches Okuyasu out, leaving open the possibility that he may be faking weakness. Losing his patience, Okuyasu has The Hand swipe half of Red Hot Chili Pepper's body into oblivion, but also erases the ground and reveals an underground cable. Red Hot Chili Pepper's manipulation has succeeded; it cuts Okuyasu's hand and drags him with it inside of the cable, but Josuke thankfully restores him back to his hand. Okuyasu recognizes his defeat and acknowledges his need to surpass his brother.
Later, Okuyasu and Jotaro leave the port to meet with Joseph while Josuke and Koichi stand guard at the port. In the boat, Okuyasu meets the elderly Joseph, who frustrates the former with his seeming lack of hearing. When Josuke defeats the user, Akira Otoishi, on the docks, Otoishi successfully escapes to the boat, disguising himself as one of the Speedwagon Foundation employees on-board. Otoishi manages to infiltrate Joseph's room and when another sailor comes, Otoishi accuses him first of being the enemy. Okuyasu is left with the decision of figuring out who the Stand user of RHCP is between the two men, while the Stand attempts to kill Joseph. Lamenting that his brother was not there to choose for him, Okuyasu spontaneously punches Otoishi in the face, before revealing that he planned on punching the both of them, and is successful in getting his brother's killer arrested.
Okuyasu then gets to see Joseph reunite with his estranged son. Joseph's cane was broken during the fight and Okuyasu proposes that Josuke fixes it but Koichi shuts him up, happy to see father and son holding hands instead.
Trouble With Rohan Kishibe
One day, Okuyasu and Josuke see Koichi entering a house instead of going to school. Knowing his tendency to get himself into trouble, they ring at the door to check on him. Koichi opens and greets his friends. He explains that he's merely visiting the manga artist Rohan Kishibe. Reassured, Josuke and Okuyasu seem to leave and Koichi even tells them good bye. However, they notice that Koichi has wounded his hand and decide to sneak inside the house. Okuyasu goes to the second story and surprises Rohan with Koichi. Okuyasu orders him to stand down or be beaten up but Rohan then brings out his insecurities about making a decision. Unnerved, Okuyasu attacks but Rohan is faster and shows him his latest chapter. Okuyasu is turned into a book by Rohan's Stand, Heaven's Door. Neutralized, Okuyasu is ordered to burn himself if Josuke ever leaves, preventing Josuke from retreating. Despite his skepticism, he grabs a lighter despite himself. Luckily, Josuke comes to the rescue and ends up being immune to Rohan's art when he's blinded by rage. He and Koichi bear witness as Josuke goes on a rampage, showing a side of him that neither have seen before and Okuyasu learns about Josuke's backstory. Though Rohan would later return as an ally, Okuyasu is left holding him in slight contempt.
A Killer in Town
After Rohan and Koichi meet Reimi Sugimoto, Okuyasu is warned about a killer lurking in town. He seldom cares about the news, more busy with admiring Reimi's photo and lamenting he wasn't born fifteen years earlier. Okuyasu is incidentally among the first to bump into Yoshikage Kira himself.
Conflict With Shigekiyo Yangu
One day, Okuyasu buys a drink but he is startled by the appearance of a short bug-like Stand. Spilling his drink on his pants, Okuyasu is furious and pursues the Stand. He eventually joins with Josuke who also has encountered the Stand; the two then see that they are dealing with a whole swarm of the same tiny Stands that gather in a park. They discover that the Stand is used by middle-schooler named Shigekiyo Yangu, or "Shigechi" for short, to gather money. Happy to make new friends with the same powers, Shigechi offers them half of his money. Okuyasu is happy to take it but Josuke declines. On the other hand, he devises a more lucrative plan. He tells Shigechi to gather all the store coupons and other stamps Harvest can find. Soon enough, the invincible trio gather enough coupons for Josuke to collect 61,000 yen. Okuyasu is overjoyed but gets angry when Shigechi claims most of the money and only hands him 10,000 yen, claiming that Harvest did all the work and thus that he deserves it. However, Josuke calms him down.
Josuke tosses the discarded lottery tickets in the trash bin, but Okuyasu stops him and says that one of the tickets could be a winning one. Josuke and Shigechi are amused at Okuyasu's optimism and Shigechi even promises that Okuyasu and Josuke truly get half of anything they win. Soon enough, Okuyasu finds a lottery ticket with a prize of 5,000,000 yen. He is overjoyed. When the trio tries to validate the ticket at a bank, the banker stubbornly tries to prove their didn't buy it but Josuke manages to overcome this. The banker must give them a money order that they can use in three days. Shigechi's greed takes over again and he claims the whole paycheck, handing 10,000 yen as a "token of friendship". This is too much for Okuyasu who punches Shigechi, insults him, and takes the order.
However, Shigechi gets angry. He sends Harvest to snatch the order and attacks Okuyasu by having Harvest cut his legs, piece by piece. Shigechi leaves, threatening to kill Okuyasu and Josuke if they pursue him. Josuke heals Okuyasu and they start to pursue Shigechi. Although Shigechi is fat, he uses Harvest as a tread to get carried across the streets and even scale a building, impressing Okuyasu. The two cooperate to have their Stand lift each other to scale the building. Despite Shigechi's action, the duo corners him on a roof. Suddenly, Okuyasu and Josuke feel dizzy and Shigechi reveals that Harvest injected alcohol directly in their bloodstream. Weakened, Okuyasu and Josuke are swarmed by Harvest. Okuyasu then gets an idea. Taking out the 10,000 yen Shigechi gave them earlier, he begs Shigechi for forgiveness and pretends to hand the money as a payment. Shigechi is lured close enough for The Hand to teleport the money order into Okuyasu's hands. Josuke proceeds to tear it apart and Shigechi sends Harvest away to gather the pieces. This gives Josuke and Okuyasu the opportunity to punch him and talk sense into him and they agree to split the prize into thirds.
Pursuing the Killer
One day at lunch time, Okuyasu and Josuke leave school in search of a decent meal. They meet Shigechi and ask him to lend them 1,000 yen which he does, reluctantly. At first they try to go to St. Gentleman to buy their famous sandwiches but arrive too late and there are no more sandwiches. They cross path with Shigechi again. Although they could go to the store Hokaben to buy bentos, a bento plus a drink each would go over their budget. Shigechi proposes that they come with him to a storage room at school to help themselves with a teacher's coffee and tea stash but they initially refuse and part ways with Shigechi. But, they do change their minds and join Shigechi in his storage room. Shigechi welcomes them but continuously forbids them to even approach his lunch. Shigechi then notices that his sandwich bag has suddenly disappeared and he accuses Okuyasu and Josuke, annoyed by this. Shigechi's search is interrupted when a teacher barges into the room, forcing the trio to flee. Okuyasu and Josuke return to class and chit-chat, only to be interrupted. A lone Harvest hands them a button before it disintegrates.
Later, Okuyasu brings his father and meets the ghost of Reimi Sugimoto in person, along with the rest of those the protagonists had met up until then. Reimi confirms that Shigechi was killed, murdered by the same man who had killed her 15 years prior. Learning this, Okuyasu is left conflicted; Knowing that he had hated Shigechi at one point, he does not know whether to feel sad or angry. Among the whole gathering, he was the first to disperse.
The Killer Makes Himself Known
Okuyasu is informed by Josuke that Koichi and Jotaro were in trouble at the shop Centipede Shoes, engaged in battle with the 'Stand' of the murder who killed Reimi and Shigechi. When they both hurry over, they find Centipede Shoes in ruins, with Koichi, Jotaro, and another man severely injured, bloody, and unconscious in the street. Okuyasu tends to Koichi and finds that he's still alive, but not breathing, urging Josuke to heal him first. The two notice the third person crawling away, and promptly stop him. Josuke fools the man into revealing himself as the serial killer, before they watch as he has his Stand cut off his own hand and escape. As the four of them give chase using the severed hand, Koichi reveals the murderer's identity as Yoshikage Kira, an office worker of 33. They are led to Salon Cinderella and find Aya Tsuji having been killed, but not before being forced to change Kira's face and fingerprints.
Battle With Yoshihiro Kira
In their search for Kira's whereabouts, the group goes to his house and encounters his late father Yoshihiro Kira in the form of his own Stand, Atom Heart Father. However, Okuyasu and Koichi were unable to help Josuke and Jotaro because they were outside of Atom Heart Father's depicted area when the fight ensued. Although Jotaro neutralized Yoshihiro and tacked him to a column, the ghost tricked Okuyasu and Koichi into believing he's left through the wood cracks. Panicking, Okuyasu opens the photo, allowing Yoshihiro to escape, with the Arrow.
I'm an Alien
One day, Okuyasu discovers a crop circle in a field. He and Josuke find a man inside of the crop circle, an eccentric individual claiming to be an alien. Okuyasu and Josuke initially laugh it off until the "alien", Mikitaka Hazekura, eats a box of tissues. Unnerved, Okuyasu wonders if he's an enemy and if he should beat him up, but Josuke dissuades him and they leave to the ice cream shop. The shop is closed, which breaks Okuyasu's heart, but the alien offers them still cold ice cream cones coming from his bag. Okuyasu still refuses to believe the man is an alien. Their dispute is interrupted when they hear fire trucks passing and the alien reacts badly to the sirens. The alien turns into a pair of sneakers and stick to Josuke's shoes; Josuke is forced to jump away, leaving Okuyasu behind.
Battle Against Toyohiro Kanedaichi
Okuyasu and Josuke find a pair of binoculars one day. The binocular is revealed to be Mikitaka. Mikitaka then informs them of the existence of a transmission tower on which lives Toyohiro Kanedaichi, a hermit with a self-sustaining lifestyle. Curious, they approach to better see but Josuke is lured inside of the tower and imprisoned. Kanedaichi's tower is a Stand, Super Fly. Unfazed, Josuke and Okuyasu try to destroy the tower's leg but Super Fly reflects the energy back at them. Okuyasu is wounded and taken out of the fight. Okuyasu then witnesses the end of the battle as Josuke and Mikitaka eventually make Kanedaichi yield.
Battle Against Yoshikage Kira
Eventually, Rohan Kishibe notices in his files the strange behaviour of Hayato Kawajiri, son of Kosaku Kawajiri. The heroes agree to meet the next day to interrogate Hayato about his father but unbeknownst to them, Kira has developed a new power. When anyone asks Hayato about Kira, Killer Queen enters the eyes and detonates their head before looping time to one hour ago. In one such loop, Okuyasu is killed with Josuke, Jotaro and Koichi.
However, Hayato manages to overcome this and calls Josuke early so that he and Okuyasu can come at the right moment to hear Kira reveal himself. Kira is forced to cancel Killer Queen Bites the Dust to defend himself. When Kira tries an unknown attack, Okuyasu displaces Kira in his direction, only for an invisible air bomb to detonate on his side. Okuyasu is mortally wounded and though Josuke heals him, he doesn't immediately wake up. In a dream, he once again meets with his brother Keicho, who asks Okuyasu where he wants to go. After a brief moment, he answers that he wants "to go back to Morioh", which results in him waking up, recovered from near-death with the assistance of Crazy Diamond. Okuyasu is surprised to see Josuke bloody and crying and continues assisting him in the battle with Kira, before Jotaro, Koichi, and Rohan come upon them. All five of them use their Stands to cripple Kira. As Kira desperately attempted to use his Stand with his broken hand, Okuyasu and others witness an ambulance accidentally crush his head, petrified by the sight.
Farewell to the Golden Heart
Okuyasu appears at the end to say goodbye to Reimi as she departs for the afterlife, claiming that he will personally be lonely without her (just like Rohan).
He is seen eating at Tonio's with Stray Cat and his father, in another attempt to cure his father of his condition. While the attempt fails, Mr. Nijimura feels better, which makes him feel okay. He is later seen telling Koichi and Josuke about a rumor he heard about Rohan getting caught shoplifting at a Kameyu shop.
Spin-Offs
The Book ~ 4th another day
Okuyasu helps in the investigation of Hanae Orikasa's death. He eventually comes across the killer Takuma Hasumi and chases him to the library, where they engage in battle. Okuyasu's experience and instincts turn out to be useful against the inexperienced Stand user, dealing serious injuries to him, but ends up being defeated regardless. Nonetheless, Okuyasu contributes to Josuke's victory by telling him how the killer fights.
Rohan au Louvre
Okuyasu makes a brief appearance, hearing Rohan's story about Nanase Kishibe along with Koichi and Josuke. Okuyasu tells Rohan he always reminded him of Mona Lisa and asked for him to imitate her pose for a photo. Rohan leaves to investigate Nizaemon Yamamura's painting without saying anything, making Okuyasu wonder if he insulted him.
Poaching Seashore
Okuyasu appears at the end of the story, again enjoying Tonio Trussardi's cuisine.
Eyes of Heaven
The story begins as an ordinary day for Okuyasu. He calls in sick and says he's caught a cold. However, Heaven-Attained DIO is overwriting reality and Okuyasu is altered into becoming a servant of DIO.
Thus, Okuyasu and a similarly brainwashed Rohan Kishibe attack Josuke and Koichi Hirose just as the two meet Jotaro Kujo from 1989 who's travelled through space and time with a part of the Saint's Corpse. Okuyasu and Rohan are beaten but Okuyasu manages to escape and disappears despite Josuke's best effort to give chase.
At one point, while the heroes travel to the universe of Johnny Joestar, in the Rocky Mountain Village, Okuyasu and Rudol von Stroheim attack the heroes. Josuke and the young Joseph Joestar team up to beat them and this time, Jotaro is able to restore them. From that point on, Okuyasu is a member of the hero party that travels through space and time to gather the Saint's Corpse.
DIO springs a trap and Okuyasu is among the 36 souls that DIO absorbs to attain even greater power. Thankfully, Jotaro manages to defeat DIO once and for all, and fate is altered for the better.
Okuyasu is last seen during the ending credits where a photo shows him, Josuke, Koichi and Shigechi who has survived.