College freshman Yūto quickly learns that the campus is buzzing about a trio of stunning sisters known as the three beauties of the incoming class. The eldest, Hanamiya Mashiro, is a poised and elegant young woman. The middle sister, Miyui, is a bright and energetic personality. The youngest, Kokonono, carries a quiet, soft-spoken charm. Each is the object of admiration for many students, but Yūto has no idea he shares a hidden past with them.

A decade earlier, Yūto was separated from his younger stepsisters following a family separation. After being raised apart and with no contact, the siblings lost all connection. Yūto himself has no memory of their faces or names, only the faint sense that he once had sisters. When he crosses paths with the three sisters at university, he is instinctively kind and helpful to them, completely unaware of their shared history. The sisters, however, recognize him immediately.

The story's central conflict and charm come from this asymmetrical recognition. The three sisters have never forgotten their older brother, and they carry a mix of nostalgia, unresolved affection, and a fierce, almost protective possessiveness toward him. They remember a gentle brother who spoiled them as children. Now, as adults, they are determined to reclaim that bond on their own terms. Each sister begins pursuing Yūto in her own way, competing for his attention while trying to keep the others from monopolizing him. Their rivalry is playful but persistent, and their advances range from subtle teasing to outright flirtation.

As Yūto navigates his new campus life, he is gradually drawn into their orbit. He treats them as friends at first, but the sisters are not satisfied with that distance. They begin to drop hints, test his reactions, and slowly reveal the truth of their relationship. The dramatic moment of full recognition—when Yūto finally realizes that the three famous beauties are his long-lost stepsisters—shifts the dynamic from a simple reunion into a romantic comedy driven by a love triangle that is actually a love quadruple.

The narrative arcs in the early volumes follow the sisters' individual strategies to win Yūto's heart. Mashiro uses her mature composure and domestic skills, often finding excuses to be alone with him. Miyui relies on her cheerful energy and physical closeness, dragging him into school events and shared activities. Kokonono, the most reserved, employs tender gestures and quiet sincerity, making her advances feel intimate despite her shyness. Each sister also contends with her own feelings of jealousy and the fear that their brother might choose another.

The setting is a modern Japanese university campus, used as a backdrop for everyday life, festivals, group outings, and the inevitable mix-ups that occur when three determined sisters try to outmaneuver one another. The tone remains light and comedic, punctuated by moments of genuine emotional warmth as the siblings rebuild a family bond that is now complicated by romantic tension. The story explores whether a childhood connection can evolve into something more, and whether Yūto can balance the affections of three women who each have a legitimate claim to his heart.