Shougo Mikadono's father has recently died, and now he must take over as CEO of Mikadono Group, his father's firm. There is just one final requirement he must meet after finishing the training to take over: he must find a girl he loves at his new school and marry her by the time he finishes high school. Shougo transfers to Miryuin Private Academy, and it appears that he has a plethora of girls to choose from, including Konoe Suruma, the class representative and his first new friend; Miyabi Kannagi, a reserved but kind girl; Rinka Kunitachi, the student council vice president; Mei Sagara, who runs a cafe and dresses like a witch; and Mana Tendou, the student council president. However, there are several complication: one of them is his long-lost half sister, and he has no idea which one, so how can he become romantically involved with any of them?