On a snowy winter night, Nasa Yuzaki, a boy who was made fun of during his childhood because of his peculiar name, encounters a beautiful girl after he received his practice exam grades for high school. When he tries to approach her, he gets hit by a truck due to his lack of attention. However, the girl saves him, and Nasa miraculously follows her at a bus stop and proceeds to confess his love for her. The girl, Tsukasa Tsukuyomi, agrees to become his girlfriend, but only if they are married first. Nasa quickly agrees to her demand and then passes out, waking up in a hospital. Nasa becomes heartbroken when he cannot find her again, until his 18th birthday, where Tsukasa suddenly shows up at his doorstep. Tsukasa goes inside with a marriage form, starting their relationship and their marriage.