Aoi Aki, eldest of the Aoi siblings, emerges from a family shadowed by concealed truths. Her mother’s early death in a traffic accident left her maternal aunt to raise Aki, Sora, and Nami as their own mother, a fiction upheld for years. Outwardly, Aki embodies perfection: admired for her beauty, athleticism, and academic prowess, she thrives as a school idol. Yet behind this polished facade lies domestic chaos—burnt meals, cluttered rooms—a stark contrast to her public image.

Her bond with younger brother Sora, forged in childhood through whispered "I love yous," spirals into forbidden territory as they age. Early advances, like a tentative shower encounter, falter against Sora’s reluctance. But persistence softens resistance; a vulnerable confession in his bedroom ignites a clandestine affair. Their liaisons, from ferris wheels to school storage rooms, blur sibling boundaries, with Aki insisting he drop honorifics for her name—a small rebellion against blood ties.

Guilt grips Aki when Sora’s grades plummet, prompting her to halt their physical relationship until he recovers academically. Complications deepen with their estranged father’s return, a man exiled years prior for his own taboo romance. Discovering the siblings’ secret, he forces separation, his death later leaving fractures. Aki withdraws to shield Sora, though their silent reunion at their mother’s grave hints at unresolved ties.

Unaware of Sora’s coerced encounters—including those with twin sister Nami—Aki fixates on guarding their secret, torn between yearning and societal judgment. The family’s layered deceptions—parental abandonment, the aunt’s maternal lie—anchor her turmoil, painting a portrait of desire entwined with inherited legacy.