"Ane no Kekkon" centers on the life of Aya Tachibana, a 29-year-old woman who has dedicated much of her adult life to raising her younger brother, Yuu, after the death of their parents. Aya works tirelessly as an office clerk to provide for Yuu, sacrificing her own personal happiness and romantic prospects. The story begins when Yuu, now a high school student, begins to feel guilty about the burden he has placed on his sister. He becomes determined to find her a suitable partner so she can finally live for herself.

The narrative explores the dynamics of sibling relationships, societal expectations, and the challenges of balancing personal desires with familial responsibilities. Aya is portrayed as selfless and nurturing, often putting others' needs before her own, while Yuu is depicted as thoughtful and mature for his age, driven by a sense of duty to repay his sister’s sacrifices. The story introduces several potential suitors for Aya, each with distinct personalities and backgrounds, creating a blend of romantic tension and emotional introspection.

As the plot progresses, Aya’s interactions with these suitors reveal her internal struggles—her reluctance to prioritize her own happiness, her fear of change, and her deep-seated love for Yuu. Meanwhile, Yuu grapples with his own feelings of inadequacy and the desire to see Aya thrive independently. The series delves into themes of love, sacrifice, and the complexities of familial bonds, presenting a heartfelt exploration of how individuals navigate their roles within a family and society.

The manga balances moments of lighthearted humor with poignant emotional depth, offering a nuanced portrayal of its characters’ growth. Aya’s journey toward self-discovery and Yuu’s evolving understanding of his sister’s sacrifices form the core of the narrative, creating a compelling and relatable story about love, responsibility, and the pursuit of happiness.