Everything has an equal and opposite reaction. For Mahiru Yanase, this means that if anything good happens to her, misfortune must follow in its wake. This theory has been proven more than true since Mahiru is constantly being compared to her kinder and far cuter twin sister, Mayo.

Long accustomed to her own unluckiness, Mahiru is thrown for a loop when she meets Aoi Satomi, a handsome classmate who takes an interest in her! However, when he confesses his feelings soon after meeting, Mahiru knows that this is too good to be true—and something bad is sure to happen as a consequence. However, Aoi's arrival might just be the key to overturning Mahiru's bad luck.