Koito Nagase, a teenage girl with chest-length brown hair, emerald green eyes, and glasses, carries herself with quiet grace. Her navy blue school uniform, dark green tie, white socks, and blue shoes—occasionally tinged dark purple in fragmented recollections—frame her delicate presence. Known for her poise and optimism, she navigates relentless bullying with resilience, attributing her classmates’ hostility to jealousy over perceived favoritism from a teacher.

Upon transferring classes, she intentionally befriends Ai Ohto, a socially isolated peer bullied for her heterochromia, becoming Ai’s sole companion. Koito’s protective outreach masks unresolved tensions: Ai later glimpses a cryptic exchange between Koito and the teacher, hinting at obscured motives.

Koito’s life ends abruptly during a rooftop confrontation where she threatens to falsely accuse the teacher of misconduct. A misstep sends her plummeting, her death initially deemed a suicide before emerging as an accident. This tragedy shatters Ai, who retreats from society and pursues the mystical Wonder Eggs to revive her friend.

Ambiguity lingers around Koito’s intentions—whether born of psychological turmoil or calculated manipulation—and her complicated dynamic with the teacher remains unresolved, fueling Ai’s guilt and quest for closure. Though Koito’s influence propels Ai’s emotional growth, their bond’s origins in mutual pain later cast doubt on its authenticity, leaving questions about affection’s role in their fractured connection.