Kei Shindou is one of the central characters in the narrative, serving as a key figure whose personal journey of unrequited love and self-acceptance drives much of her story. She is a sixteen-year-old freshman at Otobane Academy and the fraternal twin sister of Chihiro Shindou, though she is considered the elder of the two. In direct contrast to her sister’s quiet and reserved nature, Kei is outgoing, energetic, and highly competitive. She possesses a tomboyish demeanor, often acting on impulse and speaking her mind without a filter, a trait that masks a more vulnerable and insecure interior.

Kei’s background is heavily defined by a childhood incident that left deep emotional scars. When she was twelve, she took her neighbor and childhood friend, Hiro Hirono, to the beach without telling Chihiro. Chihiro, who was also close to Hiro, ran after them and was struck by a car, resulting in a severe injury that caused her long-term memory loss. Overwhelmed by guilt, Kei internalized the belief that she was unworthy of happiness, particularly regarding her feelings for Hiro. She blamed herself for stealing Chihiro’s future with him and, as a form of penance, dedicated herself to a caretaker role, waking him up, helping him with his work as a secret manga artist, and concealing her own romantic desires behind a mask of sibling-like irritation and practicality.

Her primary motivation for much of the story is her long-held, secret love for Hiro. Because of her guilt, she is unable to confess honestly and instead tries to maintain the status quo, where she is the indispensable person in his life. This precarious balance is shattered by the arrival of Miyako Miyamura, a free-spirited girl who begins to occupy Hiro’s attention. Kei’s rivalry with Miyako is fierce and desperate; she views Miyako as an invader usurping her position. In her attempts to win Hiro, Kei’s actions become more aggressive, including openly antagonizing Miyako and even deleting her text messages. Her role in this love triangle is that of the childhood friend who cannot overcome her own self-imposed barriers. Ultimately, Hiro chooses Miyako, and a subsequent injury during a crucial basketball game forces Kei to confront a double loss: the boy she loves and the sport that defined her.

Apart from Hiro, her most significant relationship is with her twin sister, Chihiro. The accident created a rift between them, as Kei’s guilt prevented her from feeling she could be a proper sister. Their reunion and reconciliation form a pivotal moment in her development. Later, she meets Kyosuke Tsutsumi, a passionate filmmaker who becomes infatuated with her image. Initially, Kei views Kyosuke as a mere distraction or a substitute for Hiro, but his unwavering dedication to his dream of making films slowly helps her heal. Through Kyosuke, she learns to accept that her past feelings for Hiro were not wrong and that she deserves to move forward. She eventually lets go of her self-blame and begins a genuine romantic relationship with him, finally breaking free from the shadow of her childhood trauma.

Throughout the story, Kei is notable for her athletic prowess. As a freshman, she is the star player on the school’s girls’ basketball team, a role that highlights her physical energy and determination. However, this strength is contrasted with notable weaknesses; she is a notoriously bad cook, a trait she shares with her sister, and she struggles academically in every subject except physical education. Her development is a gradual process of dismantling the walls built by her guilt, transforming from a jealous and self-punishing girl into someone capable of accepting love and forming a new identity beyond her past losses.