On a snowy winter night, Nasa Yuzaki is lying on the street bleeding. During the time he believes he is going to die, he recalls his life, remembering how he was ridiculed for his unusual name and how he devoted his life to studying, wanting to attend an elite school. But before he was set to take the entrance exam, he was hit by a truck when he crossed the street trying to speak to a girl named Tsukasa Tsukuyomi. However, Nasa survives due to her intervention. After regaining consciousness, Nasa chases after Tsukasa, wanting to go out with her as gratitude for saving his life, and Tsukasa agrees only if they get married when they are old enough to do so...