Saki Nagatsuka, class president of 6-C at Keishin Academy, initially hesitated to join the girls' basketball club, fearing her glasses would interfere. Maho Misawa convinced her by providing a custom eye-guard for game protection. She possesses long blue hair, typically worn in two braids, and wears spectacles, though she often lets her hair down during basketball while using the eye-guard. Standing 148 cm tall, she was born on July 1 (Cancer, blood type O).

Level-headed and composed, Saki acts as a stabilizing counterbalance to Maho's hyperactive tendencies, monitoring her behavior and intervening to prevent conflicts, especially between Maho and Natsuhi Takenaka. While generally rational, she prioritizes sensibility over logic concerning her family's okonomiyaki restaurant or Maho's boundary-crossing. She exhibits tsundere traits, struggling to openly admit her desire for praise from coach Subaru Hasegawa. Her composed nature earned her the nickname "Ice Age" from school nurse Touko Hatano, and "Speed Queen" for her playing style.

On the court, Saki plays as shooting guard (jersey number 6), later transitioning to point guard. Though lacking Tomoka Minato's shooting talent or Maho's athleticism, she compensates with strong decision-making and situational analysis. This shift allows Tomoka to focus more on scoring. Her calm strategic assessment proved crucial against Suzuridani, enabling the team to adapt to defensive tactics.

She works part-time as the "Kanban girl" at her family's okonomiyaki restaurant, assisting with orders and promotion. This background explains her serious, focused demeanor when cooking or discussing okonomiyaki.

Across official media, including all anime seasons, the "Tomoka no Ichigo Sundae" OVA, manga adaptations, and video games, Saki becomes increasingly invested in the team's growth. Her relationships evolve, maintaining her role as Maho's primary supervisor while gradually expressing more openness within the team, though she retains her tsundere tendencies regarding Subaru.