Shiona Kujirai, initially known only as "Basketball Sempai," is a third-year student and president of the Kaminoki High Basketball Club. She sports fairly short blue hair and is often seen in her basketball uniform, prone to nervous cold sweats due to inherent shyness.

Her story begins when Kohane Hatoya, Uki Sawatari, and Hizume Arima accidentally gather during her club's gym practice, leading to her first contact with the forming Cheer Association. Later, learning the Cheer Association accepts support requests, she asks them to cheer at her team's match against a rival club. Their performance energizes her team to victory. Impressed, she and the Basketball Club subsequently invite the cheer squad to their prefectural-level game.

Despite her basketball skill and leadership, Shiona struggles to express gratitude openly. Instead of direct thanks for the cheer squad's support, she discreetly arranges for the Home Economics Club to provide a meal as appreciation, highlighting her difficulty with face-to-face emotional expression. Her friendship with the Home Economics Club president, a fellow third-year, is noted.

Shiona gradually integrates more into the school community, attending events like the cheer competition to support the Cheer Club. Her real name, Shiona Kujirai, is revealed later in the narrative, specifically in chapter 37 of the manga, as she nears graduation and transitions from her basketball role. Her surname incorporates the kanji for "whale" (鯨, kujira).