Yusuke Okuma (Japanese: 大隈優介, Okuma Yusuke) is a second-year student of Seiin High School. He serves as a middle blocker on the boys' volleyball team. A former member of the rugby team, he was invited to the volleyball team by the vice captain, Misao Aoki.
Okuma has blonde hair slicked back from forehead and brown eyes. He stands at 187 cm (6'1").
During matches, Haijima wears his volleyball uniform – a navy blue jersey with sky blue and white stripes on the sleeves and corresponding navy blue shorts. His position number, 10, and the name of the school are printed on the front of his jersey in sky blue text with a white outline. On the court, he wears white kneepads and white volleyball shoes with black accents.
- Okuma was initially a member of the Seiin rugby team. However, Aoki offered him a position on the volleyball team after seeing his performance during the school's sports festival.
- His given name Yusuke means "tenderness", "excellent", "surpass" (優)(yu) and "assist", "mediate", "shell" (介)(suke)
- His surname Okuma means "big", "large" (大)(o) and "corner", "recess" (隈)(kuma).