The story begins in a walled, circular town called Glie, where a winged girl named Rakka emerges from a giant cocoon. Welcomed by the Haibane—beings with small grey wings and halos—she learns her new existence is peaceful yet melancholic. The Haibane live in Old Home, an abandoned school, and survive by working in the town under strict rules: they must use second-hand items, cannot handle money, and must never approach the massive Wall surrounding the town.Rakka struggles to integrate, haunted by fragmented, terrifying memories of her life before. Unlike others who adapt quickly, she is burdened by a sense of sin. This internal darkness manifests physically when her wings turn a menacing charcoal grey, a condition known as the "Day of Torment," signaling that she is withdrawing from her community and spiraling toward despair. Meanwhile, her friend Reki, the eldest at Old Home, hides her own deep-seated trauma. Reki suffers from the "Sin of Indifference" and fears her own upcoming Day of Torment, desperately trying to protect everyone else while secretly believing she is unforgivable and destined to be cast out as a "Sin-bound Haibane"—one whose wings turn entirely black and who loses her mind.As Rakka sinks deeper into isolation, she experiences a profound spiritual crisis. Her turning point arrives when another resident, a young girl named Kuu, mysteriously experiences her "Day of Flight"—the ultimate departure where Haibane shed their cocoons entirely and vanish over the Wall to an unknown destination. Kuu’s departure devastates Reki but inspires Rakka to seek redemption. Rakka realizes that true peace cannot be found by running from her past, but by accepting her flaws and forgiving herself. Through the guidance of the town’s mysterious Communicants—mute elders who interpret the rules—and her own self-reflection, Rakka’s wings slowly heal, turning a pristine, luminous white.With her sanity restored, Rakka dedicates herself to saving Reki, whose wings have already blackened with sin. Rakka uncovers the truth of Reki’s past and realizes that Reki is terrified of being left behind. In the dramatic climax, Rakka confronts Reki, offering her
unconditional love and forgiveness. This emotional breakthrough shatters Reki’s despair. Her black wings fall away, and she finally experiences her own Day of Flight, transcending the Wall. Rakka is left behind in Glie, now a mature and compassionate member of the community, tasked with guiding the
next generation of newly hatched Haibane who emerge from the cocoons, carrying forward the cycle of redemption, acceptance, and hope.