Koichi Hirose (広瀬 康一 Hirose Kōichi) is the deuteragonist of the fourth part of JoJo's Bizarre Adventure, Diamond is Unbreakable. He also appears briefly as a minor ally in the fifth part, Vento Aureo, assisting Giorno Giovanna in the fight against Polpo's Stand, Black Sabbath.
Koichi is a meek first-year highschooler who finds himself embroiled in the world of Stand users as he befriends Josuke Higashikata. Koichi eventually becomes a Stand User and wields the sound manipulating stand Echoes.
Diamond is Unbreakable
Koichi is a teenage boy of average build, 157 cm (5'2") tall, though he's typically depicted as a lot shorter. He wears a notably unmodified student uniform, otherwise preferring leisure wear.
Koichi first keeps his light hair neatly combed back. During his confrontation with Tamami, it gains the tendency to rise into spikes when he is excited. Towards the end of his confrontation with Yukako, he suddenly cuts his hair, producing a flat-top, which spontaneously grows out again into spikes during his battle with Yoshikage Kira. The color of his hair varies throughout the media, the most common schemes being blond, blue, or silver.
Koichi's jacket is replaced with a much longer double-breasted variation featuring metallic wristbands and the Roman Numeral for three (III) on each side of his collar.
Koichi is an amiable, but meek youth who undergoes an exceptional degree of character development over the course of Diamond is Unbreakable, becoming more assertive throughout many confrontations with evil Stand users. His growth is best represented by the metamorphosis of his Stand, Echoes.
One of Koichi's constant traits is his friendliness and overall politeness toward any stranger and acquaintance. Having a gentle heart, Koichi usually doesn't seek to harm his opponents, notably having saved Yukako from death even though she wanted to kill him before, and briefly fighting Giorno Giovanna without the strength to kill, which inadvertently saved him. However, Koichi's friendliness disappears on the rare occasions he is angered, and he becomes more abrasive, violent and vulgar.
Complimenting his childlike appearance, Koichi also possesses a rather cheerful personality. He finds wonder in the littlest and most mundane things (such as his new bike, a famous mangaka living in town, finding an error in a map, etc.), and has little trouble befriending people. Because of this, he is usually easily pressured into an interlocutor's demands, such as Tamami Kobayashi effortlessly extorting him, or Rohan pushing him into spending time with him. Much like any ordinary teenager, Koichi is interested in more accessible distractions. He is a great fan of Rohan Kishibe's manga Pink Dark Boy and plans to visit Disneyland Paris but expresses no interest in "old" countries such as Italy.
Another one of Koichi's primary characteristics is his courage and associated virtuousness. As revealed by Heaven's Door, Koichi is described as cowardly, but courageous when push comes to shove. True to that assertion, Koichi is very prone to express anxiety, fear, and despair at various setbacks, such as his battles against Yukako, Rohan or Sheer Heart Attack. Terunosuke states that when Koichi is scared he blinks twice. In addition, Koichi mentions during the Atom Heart Father arc that he has claustrophobia. Still, Koichi soldiers on and braves danger despite his fears.
Initially weak-willed, acquiring a Stand and fighting others made him more confident in himself and assertive, going from being bullied by upperclassmen to facing down and taunting Yoshikage Kira while on the verge of death. By Vento Aureo, Koichi has grown into a confident youth who, while still prone to bouts of panic, could enter a Stand fight without qualms.
The mix of his gentleness and courage make Koichi an extremely likable individual, earning the friendship and respect of the vast majority of the cast including Josuke Higashikata, Tamami Kobayashi, Toshikazu Hazamada, Rohan Kishibe, Yukako Yamagishi, Aya Tsuji, and Jotaro Kujo.
Koichi is a relatively perceptive individual, able to make quick and decisive moves in a fight, sometimes at the cost of being too imprudent. For the most part, Koichi tries to analyze his situation before acting, notably due to how weak his Stand is at the start of the series and the severe limitations of his powers, but sometimes misses a critical consequence of his actions.
After a difficult start in his relationship with Yukako, due to her kidnapping Koichi, he eventually fell in love with Yukako's tough and unforgiving personality. His love was such that he was willing to be blinded forever in case Yukako became ugly, so as to ease her pain.
- Main article: Echoes
Koichi's Stand, Echoes, starts off with ACT1 only. However, the Stand evolves through the narrative of Diamond is Unbreakable, giving Koichi new abilities to use. Throughout his battles against Stand users such as Yukako Yamagishi and Yoshikage Kira, Echoes gains ACT2 and ACT3. Koichi is able to willingly call upon Echoes' previous ACT forms at will and utilize their unique abilities.
Echoes ACT1 enables him to write on any surface, causing the words or onomatopoeia to continuously repeat at various volumes.
Echoes ACT2 enables him to write a sound effect on any surface. If the word is touched, a special effect related to the sound effect is activated.
Echoes ACT3, a humanoid Stand, facilitates conventional melee attacks and the ability to "freeze" targets by ascribing them unbearable weight.
Thanks to Echoes' three forms, Koichi is presented with a wide array of options. For direct combat, Koichi favors using his latest ACT, almost exclusively using Echoes ACT3 when he unlocks it despite ACT2's potential for versatility. With Echoes ACT3, Koichi makes ample use of his weight increasing power to immobilize enemies.
Koichi also regularly uses ACT1 as a scout, using its great range of 50 meters to watch his surroundings.
- Josuke Higashikata: One of Koichi's best friends, the two quickly got along the first moment they met. Koichi admires Josuke and looks up to him while considering him a kind strong person. In turn, Josuke also relies on Koichi during battles and is impressed by his bravery. Josuke is willing to help him whenever he can, such as when Yukako goes after Koichi.
- Okuyasu Nijimura: The two met on bad terms as Okuyasu slammed some doors between Koichi's neck nearly choking him. However, they moved on from that and became friends. While Koichi and Okuyasu do not have much interaction, they've shown to care for each other's well-being. Okuyasu was concerned when Koichi was kidnapped by Yukako and during the Red Hot Chili Pepper arc, Koichi was sympathetic and comforting to Okuyasu's plight and desire for vengeance against Red Hot Chili Pepper. Nonetheless, Okuyasu is mildly jealous of Koichi's relationship with Yukako, as Okuyasu himself hasn't had a girlfriend.
- Jotaro Kujo: Koichi looks up to Jotaro as a strong ally, although he is put off by Jotaro's aloof temperament. Their cooperation during the Sheer Heart Attack story arc had Jotaro act as a mentor figure to Koichi, who came to really respect Jotaro's prowess in battle. In addition, Jotaro also grows to see Koichi as a good friend and a reliable person, enough so that he chose him to go to Italy and investigate Giorno Giovanna.
- Rohan Kishibe: Koichi first admired Rohan as a talented mangaka, but his view changed quickly upon their first meeting when he and Toshikazu Hazamada went to visit Rohan. While Rohan liked Koichi and grew to see Koichi as his first (and possibly only) true friend, he was still abrasive and pushy, notably pressuring him to accompany him on two occasions, and Koichi tolerated less and less the worst sides of Rohan's arrogance as he gained confidence and he was overall a positive influence on Rohan's attitude. At the end of Diamond is Unbreakable, one reproachful look from Koichi was enough for Rohan to yield and confess an attachment to Reimi Sugimoto.
- Yukako Yamagishi: When Yukako first confessed her feelings to him, Koichi was happy but quickly lost interest upon learning of her obsessive personality, made worse when she kidnapped him. He managed to defeat her and remained somewhat frightened of her. However, during the Cinderella arc, Koichi sought to reconcile with her and grew attracted to her forceful and aggressive personality, ultimately the two became a couple. Koichi's affection for Yukako was such that he was willing to blind himself if Yukako ended up being ugly due to Cinderella's power in order to ease her pain.
- Reimi Sugimoto: The two met when he and Rohan stumbled upon the haunted alleyway she resided in. While initially scared upon hearing she was a ghost, he quickly sympathized with her after hearing her tragic story and promised to find her killer so she may rest in peace. He later bids her farewell when she ascends to heaven and was rather saddened with her parting. He also gave Rohan a reproachful look so he would admit he would miss Reimi too.
- Tamami Kobayashi: Initially Tamami tried to scam Koichi with his stand, but Josuke and Okuyasu intervened. When Tamami tried to involve Koichi's family, Koichi got so angered he awakened his Stand and beat Tamami. Since then, Tamami has become afraid of Koichi but also genuinely respects him. Their relationship has been described as a one-sided boss-subordinate relationship.
- Toshikazu Hazamada: Koichi and Josuke fought him and quickly defeated him. Afterward, Hazamada somewhat bonded with Koichi over their mutual interest in Pink Dark Boy and the two went to visit Rohan's place. Their relationship has been described as a one-sided friendship.
- Aya Tsuji: While the two had little interaction, Aya grew to respect Koichi's determination when she saw his willingness to blind himself if he couldn't help Yukako through the trial Aya put her through. He was also saddened when Kira killed her.
- Family: While not much interaction was shown with his family (which consists of his parents and older sister), when Tamami tried to use them to get revenge on Koichi, he became enraged enough to beat Tamami by awakening his Echoes ACT1 Stand, demonstrating that he cared for them. His relationship with his father is never shown but is presumed to be good.
- Giorno Giovanna: Koichi was sent to investigate Giorno by Jotaro, and Giorno did his best to avoid Koichi even turning his suitcase into a frog. However, over time Koichi grew to see Giorno's noble soul. He reports to Jotaro after the trip, but he convinces Jotaro that Giorno is a good person.
The Book: JoJo's Bizarre Adventure 4th Another Day
- Chiho Futaba: Koichi firstly meets Chiho in Thorn Palour while studying with Yukako, and gets to know her through Yukako's introduction. He runs into Chiho again about 5 months after Takuma Hasumi's case. Surprised to find out that Chiho is pregnant with Takuma's baby, Koichi decides to keep this encounter as a secret and sees Chiho leaving Morioh, sending his wishes to her.
- Takuma Hasumi: After discovering Trinita and Hanae Orikasa's corpse, Koichi and Rohan start investigating to find the culprit, who is ensured to be a Stand user. Later, Koichi runs into Takuma at the hallway in his high school, along with Josuke and Okuyasu, without realizing Takuma is the culprit and has already sensed their actions.
- Yoshikage Kira: Koichi, after learning of Kira's crimes, came to deeply loathe him to the point he would attack him on sight. Kira, on the other hand, came to somewhat praise Koichi's ability for being able to track him and then indirectly humiliate him in public, which he made sure to pay back with a beating. When Koichi humiliated Kira a second time, demonstrating how careless the serial-killer could be, Kira was enraged and came to detest Koichi, being happy at the prospect of Koichi dying.
- Terunosuke Miyamoto: While there is little interaction between the two, Koichi hated Terunosuke for taking him hostage and trying to kill him and Josuke.
Chapters / Episodes
- Koichi's name and basic appearance appear to have been taken from the main character and a narrator of one of Araki's earlier works, Cool Shock B.T.
- Koichi's surname, "Hirose," is derived from the Hirose River (広瀬川 Hirose-gawa), located within the city of Sendai, Araki's birthplace.
- Although it's never been explained why, Koichi's enemies tend to shrink in size after he beats them. This is not shown in the anime for consistency; Koichi's enemies are already short when they're introduced.
- Koichi's stand is named after a track by Pink Floyd, just like Josuke's stand. This is a distinction he shares with his alternate-universe parallel Yasuho Hirose, who shares Prince references as stand names with her respective universe's Josuke.
- Koichi's voice actor in the TV anime, Yuki Kaji, also voices Johnny Joestar in the Bandai Namco video games. Similarly, his Bandai Namco games voice actor, Romi Park, voiced Giorno Giovanna in the PS2 video game GioGio's Bizarre Adventure.