The protagonist, Haruna Iba, is a university student in Kitakyushu. One evening, she visits the general hospital where her brother works. Her brother, Masato, a surgeon, had just finished operating on an emergency patient when he said something strange to her: "The locket pendant the patient had contains a photo of me as a child. Why is that?" Soon after, they learn an unexpected truth from their parents—the woman who had been brought in, Yumiko Sakurai, is Masato's biological mother. As their father reveals more about the past, they are further shocked by the revelations.