The shocking news hits our protagonist, Tokieda Nao, that she is now engaged to a man she never planned to marry. Her father's struggling company has led to this unexpected arrangement, leaving Nao feeling unhappy and forced into this decision. However, her life takes an unexpected turn when she attends a newly co-ed high school after only attending all-girls schools before. With a small percentage of female students, Nao knows her fiance attends the school but has no idea who he is. Meeting two fascinating male students, the grumpy Sakaki Mitsuru and stunning Toono Minori, whom she mistook for a girl, Nao becomes determined to uncover her fiance's identity with only five clues: a mole near their hip, a flower-shaped birthmark, a past childhood connection, and fear of heights. As more than one boy meets the criteria, Nao becomes intrigued by the challenge of solving the puzzle to learn the true identity of her fiance. Will she be able to figure it out?