Tooru Oikawa and Iwaizumi Hajime

Oikawa has dark brown hair that is swept outwards and eyes of the corresponding color. Many people find him attractive, to the point where several girls follow him around. Oikawa frequently smiles or grins, although Iwaizumi notes that these expressions are rarely genuine. He tends to make victory signs or large waving gestures, which are often accompanied by broad smiles or a wink. Another trademark expression of his is sticking out his tongue while smiling and winking.

Oikawa is of decent height for a volleyball player, standing just over six feet. While on the court, Oikawa wears the standard aqua and white Aoba Johsai High uniform emblazoned with the number one. He also wears dark gray athletic shoes with blue details. He wears a white kneepad on his right leg, contrasting with the black one worn on his left and by the other players in the series. At other times, Oikawa dresses in the Aoba Johsai uniform, which consists of khakis with dark brown detailing, a cream-colored vest, a dark red tie, a lavender button-down shirt, and a white blazer. During practices, he wears an aqua shirt and white shorts. During the finals match between Karasuno and Shiratorizawa, Oikawa is shown to wear glasses but it's unknown if he truly needs them or not.

Post-timeskip, Oikawa appears mostly the same although his hair is noticeably shorter, and he has developed a slightly more muscular build. Despite his flirtatious nature (which makes him famous amongst female students, much to Tanaka and Nishinoya's envy) and childishness, Oikawa is an excellent, well-rounded player and is extremely serious about volleyball. He's known to have a "disgusting personality" amongst both opponents and his own teammates because of his smug and outwardly flippant attitude. Oikawa also frequently makes cheerful remarks but follows up with serious or intimidating afterthoughts. He is extremely intelligent and cunning and easily figures out both his teammates' and opponents' weaknesses.

However, on more than one occasion, Oikawa has been very attentive and caring towards others, but this is mostly seen with his teammates or people like Hinata while in Brazil.

Oikawa is ambitious and one-track-minded, but it's shown that he also has feelings of inferiority towards those he deems as naturally better than him, such as Ushijima and Kageyama. This is one of the main reasons he is known to push himself so hard. Oikawa also holds a grudge against Kageyama, whom he mockingly calls Tobio-chan. This is due to his feelings of inferiority surfacing when compared to Kageyama, who has been hailed as a genius setter since their time spent at Kitagawa Daiichi. Kageyama and Ushijima can also unintentionally bring out the more childish or rash aspects of Oikawa's personality.

To match his ambition, Oikawa works extremely hard and often endures vigorous solo practices after his normal practices with the team. In addition, Oikawa spends time at home watching past games of his rivals in order to observe their movements and patterns ahead of time and strategizing how to defeat them. Despite that, he still takes time off on Mondays for rest.

It was seen post-timeskip that Oikawa has had thoughts of giving up on volleyball, but whenever that thought occurs, something really fun comes along to remind him why he loves it so much. Showing that while he has seemingly endless ambition, he does occasionally have doubts, though they never overwhelm him. Since early childhood, Oikawa is shown to have been heavily involved in volleyball. He was occasionally shown watching matches on television or playing the sport with Iwaizumi when they were still kids. When he was a little older, Oikawa and Iwaizumi attended a match between Japan and Argentina where Oikawa would become inspired to become a setter after seeing how the Argentina setter, Jose Blanco, was able to help the ace player get back on his game when he had started struggling during the match[2].

After this interaction, Oikawa is seen investing himself more into volleyball and appears to have been trying jump serves since he was young. Because of the time he put into his abilities, Oikawa was said to have been a highly skilled player by the time he began attending Kitagawa Daiichi. However, Oikawa began to struggle when his team began playing against Shiratorizawa Junior High and it was in particular playing against Ushijima that caused Oikawa distress and the start of his rivalry with the Shiratorizawa ace.This only became worse when Tobio Kageyama began attending Kitagawa Daiichi and almost instantly started to gain more attention than Oikawa thanks to his higher skill set, natural athletic abilities, and being labeled as a prodigy at such a young age. Aware that Kageyama could potentially surpass him, Oikawa began behaving poorly toward the younger setter and constantly refused to teach him any new skills. After nearly striking Kageyama in a blind rage, Oikawa was able to get back on track thanks to help from Iwaizumi. This led to him being able to better focus his plays to bring out the best of each of his teammates and was eventually able to help Kitagawa Daiichi place second in the middle school tournament after Shiratorizawa. At the same time, Oikawa received the Best Setter Award and soon after would join Aoba Johsai.

Iwaizumi has dark, spiked-up hair, and thin 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 Aoba Johsai uniform with number four on it. He is otherwise shown wearing an Aoba Johsai 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.

Post-timeskip, Iwaizumi's appearance has changed very little with the only exception being his hair is slightly shorter.

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 Aoba Johsai team to look up to and respect him. His underclassmen often gravitate towards him, and he is seen giving calm and light-hearted advice to Kindaichi, which can contrast to how he treats Oikawa. He is also very respectful and does not treat his rivals coldly, as Kageyama still treats him respectfully and Iwaizumi has acknowledged his skills.

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" fish in a book to make fun of Oikawa with.