Hajime Iwaizumi (Japanese:
Iwaizumi has dark, spiked-up hair and slightly thicker than average eyebrows. His eyes are dark brown in the manga, olive green in the anime adaptation, and grey in the Haikyuu!! smartphone game. His hair is black in the manga and in the Haikyuu!! smartphone game, but dark brown in the anime. More often than not, he's shown to hold a serious or irked expression.
While playing volleyball, Iwaizumi wears a standard Aobajohsai uniform with number four on it. He is otherwise shown wearing an Aobajohsai school uniform consisting of khakis with dark brown details, a lavender-colored button-down shirt, a dark red tie, and a white blazer. Iwaizumi's uniform appears to be missing the cream-colored vest that goes with the rest of the uniform and appears to be slightly disheveled, with his tie loose around his neck and his shirt left untucked.
In the anime adaptation, Iwaizumi is seen wearing an outfit which consists of a pair of jeans with an oversized dark blue denim jacket over a grey hoodie.
Iwaizumi is a stubborn but reliable teammate, often filling in Oikawa's spot as a morale booster if needed. He acts supportive to all, including Tobio Kageyama, and calls Oikawa out for his childish antics. He often resorts to violence with Oikawa whenever he teases or provokes him, but this does not change the fact that he cares immensely for him, as shown when he makes an effort to stop Oikawa from either working too hard or losing confidence. Iwaizumi's firm-yet-caring attitude has led some members of the Aobajohsai team to look up to and respect him.
It is also seen through some extras by Furudate that while Iwaizumi can be strong and intimidating he also has quite the goofy side where he loves monsters and gets excited when he finds an "Oikawa" (a type of fish) in a book to make fun of Oikawa with.
Iwaizumi is Aobajohsai's ace, and his spikes are incredibly strong. He is a dependable player with faith in his own abilities, which leads Oikawa setting to Iwaizumi whenever he feels that he's in a pinch. He is shown to have solid receives; often getting the ball when Shinji Watari, Seijō's libero, is unable to. Iwaizumi stated that when he was little he only found spiking to be fun, but as he has gotten older he's grateful that he knows the "thrill" of receiving his opponents' flawless hits. It has been noted by Keishin Ukai that Iwaizumi has a powerful serve. Being hit continuously by his and Oikawa's serves throughout a match can be incredibly taxing on their opponents. He is also fearless enough to exploit Koganegawa's technical flaw as a blocker despite his height.
Jumping Reach: 327 cm
- Favorite food: Agedashi tofu
- Current concern: "Just 1cm more..or 7mm, at least..!" (In regard to his height.)
- He is the oldest in Seijō out of all the members whose birthdays have been revealed.
- He is very athletic as shown by him beating Kyōtani in several events such as running, batting, and arm-wrestling.
- His star sign is Gemini.
- When combined, Iwaizumi and Oikawa's first names (Hajime and Tōru respectively) form "一徹" meaning "obstinate" or "dauntless".
- Iwaizumi's birthday is the death date of Alexander the Great, matching with Oikawa's birthday which is the birthdate of Alexander the Great.
- Iwaizumi is one of the few characters whose color palette varies in the manga to anime. In the manga, his hair is black and his eyes are dark brown, but in the anime, his hair is dark brown and his eyes are green.
- Iwaizumi's skills have been commended by Karasuno's players and coaches and his total stats add up to the same total as Ushijima, one of the top 3 aces in Japan.
- It has been implied in the Seijō extra that Iwaizumi and Oikawa might be attending different universities, although the phrasing is vague enough it's unclear. Furudate has yet to explicitly state whether they will be attending the same school.
- While Iwaizumi is taller than average, he's the shortest of the Seijō third years and appears to find frustration in this. In the Haikyuu Cross Team Match game, Iwaizumi states his goal is to grow to 185 cm so he'll be taller than Oikawa (who responds that he will push on Iwaizumi's pressure points so he can't grow taller than him).
- There is a running gag that whenever he and Oikawa are in the same camera shot, Oikawa will block Iwaizumi's face somehow, whether it be him holding a peace sign in front of him, or standing directly in front of him.
- Iwaizumi was voted the top wing spiker by readers in the "Best Lineup" poll with 1240 votes.
- In the Cross Team Match game, Iwaizumi says he used to capture cicadas during childhood but he always let them go afterward (when asked, he said cicadas had a short lifespan so he took pity on them).
- He's not very good at drawing.
- In Haikyuu's first popularity poll, Iwaizumi placed 11th with 3,097 votes. In the second, he rose to 9th with 6,111 votes.
- Hajime (一) - One
- Iwaizumi (岩泉) - Rock (Iwa) Spring/Fountain (Izumi)