Yuni Kuroba (黒羽 祐仁, Kuroba Yuni) is a first-year student at Seiin High School and a member of the boys' volleyball team who serves as an outside hitter and their ace.
Kuroba has shaggy black hair and golden yellow eyes. In middle school, he stood at 175 cm (5'9") but grew to 184 cm (6'0") by the time he entered high school.
During matches, Kuroba 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, 7, 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 volleyball shoes with black accents, and no kneepads.
Yuni is a semi-cheerful boy. He becomes passionate about volleyball, wanting to be the ace of the team. According to his cousin, he gets too cocky when he gets complimented
Yuni and Hajima used to be childhood friends before Haijima moved away to Tokyo. During middle school, Haijima moves back and reunites with Yuni. Yuni is in the volleyball club; however, he doesn't play. Haijima joins and the team actually starts playing/practicing. They play at their first competition and at the 2nd game, Yuni gets anxious and forgets how to play. Yuni then finds out about Haijima's past through his cousin, Yori. This causes Yuni to play behind his back and the team to fall apart.
- The name Yuni means "help (divine help/divine protection), assist" (祐) (yu) and "benevolence, compassionate" (仁) (ni).
- Yuni's surname Kuroba means "black" (黒) (kuro) and "feather" (羽) (ha/ba).