Hajime Iwaizumi

Height: 179.3 cm / Weight: 70.2 kg / Highest jump reach: 327 cm / Birthday: June 10 / Favorite food: Agedashi tofu / Recent concern: Just another 1 cm... no, at least 7 mm...!

A third-year WS and vice-captain of the Aoba Johsai High School volleyball team. His jersey number is 4.

An ace spiker. He possesses both power and technique, and has the mental strength to make crucial plays. Having played volleyball with Oikawa for many years, he shows stable combination plays, described by Kageyama as having "perfect harmony." Called "Iwa-chan" by Oikawa, who has been his friend since elementary school, Iwaizumi often receives teasing from him but also dishes out harsh words in return. During middle school, when Oikawa became obsessed with playing alone due to the defeat by the genius Ushijima and the arrival (enrollment) of the genius Kageyama, Iwaizumi reminded him that "a team of six that is strong together wins," emphasizing the importance of team play. He is the only person who can scold Kyotani over his head. After losing in the Spring High preliminaries, he encouraged Oikawa by saying, "You're my proud partner and an amazing setter. That won't change even if the teams do."

In the final match of the Spring High preliminaries, he praised his junior Kageyama for his quick reaction to Hinata's sudden change of tempo in Karasuno High School's final attack that secured their victory. After graduating from high school, he became a university student and went to the United States to meet Ushijima's father, Takashi Sora, where he was surprised to learn from Ushijima that Sora was his father. During the 2021 Olympics, he was working as an athletic trainer and became the athletic trainer for the Japanese national team.