Shougo Mikadono finds himself in a bizarre predicament upon his father's passing. In order to inherit his sizable fortune, Shougo must enroll in a peculiar school and marry a suitable girl. However, his seemingly straightforward task takes a complicated turn when he discovers that one of the girls could be his long-lost sister. Now, Shougo must navigate the tricky path of romance without unknowingly breaking moral boundaries. With the identity of his sibling concealed among the potential brides, the stakes are high as secrets unravel in unexpected ways.