After his father's death, Shougo Mikadono inherits Mikadono Group and becomes its leader. However, he must fulfill a condition to cement his position - he must find love in high school and marry the girl before he graduates. To achieve this, Shougo enrolls in Miryuin Private Academy where he interacts with several girls, such as Konoe Suruma, his first friend, Miyabi Kannagi, a kind but distant classmate, Rinka Kunitachi, the student council vice president, Mei Sagara, a witch-dressed café owner, and Mana Tendou, the council president. However, here's the twist - one of these girls is his long-lost half-sister, and he doesn't know which one. The situation becomes complicated, and Shougo must navigate his emotions carefully to avoid any inappropriate relationships.