Synopsis: Binetsu Kuukan

Amane Nakanose is thrilled when she hears that her mother wants to remarry and gain a younger brother. However, when Naoya Akasegawa introduces himself as her brother, Amane is disappointed to find out that he is only three days younger than her. Naoya had also envisioned an older sister who is very different from Amane's demeanor. Naoya is met with indifference and is forced to refer to Amane as "onee-chan," causing him to attempt to adjust to his new life with his sister. Despite Amane's aloofness, Naoya begins to see her softer side. With renewed hope, he decides to make the most of their new family dynamic.