Kazumi Endo is a first-year student who serves as the manager of the soccer club at Kakegawa High School. She is a childhood friend of the three main male characters, which places her in a unique position to understand their history and individual struggles with the sport. Described as something of a tomboy, Kazumi is a genuine football enthusiast who takes great pleasure in watching games, especially when her three close friends are playing together.

Her most defining trait is her fierce dedication to her role and her team. Kazumi is regularly seen on the sidelines, cheering for the players and offering them support. She is also notably protective of the club, taking it upon herself to act as a barrier between the team and the crowds of fangirls who try to get too close. This determination extends beyond just managing daily activities; she is proactive in trying to get her friends back into the sport. When Kenji and Kazuhiro had quit playing football, she worked alongside Toshi to persuade them to return to the pitch, motivated by her love of watching them all play together.

Regarding her personal relationships, Kazumi is at the center of a romantic triangle. The character Kazuhiro is shown to have romantic feelings for her. However, her own affections lie with their other friend, Toshi. This creates a rivalry between Toshi and Kazuhiro, although Toshi himself does not appear to reciprocate her romantic interest or show much awareness of her feelings, viewing her primarily as a friend. Her key relationships are defined by this dynamic: her loyalty to the team as a manager, her protective friendship with all the players, her romantic interest in Toshi, and her admirer in Kazuhiro.

Within the overarching story, Kazumi's role is that of the dedicated club manager and a source of emotional support. Her motivations are closely tied to her friends' success and happiness; she wants to see the team succeed and to restore the joy of playing football that the three boys shared in the past. Her development is shown through her unwavering commitment to the soccer club, acting as an emotional anchor and a buffer against outside distractions, ensuring her team can focus on their goals for the national championship. Her notable ability is not athletic, but social and organizational: she is adept at managing the club's affairs and, more distinctively, at controlling the crowds of female admirers to keep the team's environment stable.