When Takuma Kakinouchi (Shuhei Nomura) was 8-years-old, he spent time in the hospital. He made friends with Mayu Taneda (Hinako Sakurai) who was the same age as him. One day, they got out of the hospital and visited a park. There, Takuma Kakinouchi and Mayu Taneda promised that they would marry each other. They had no doubt that they would have a future together.
7 years later, Takuma Kakinouchi entered a prestigious high school at the age of 15. During the high school welcoming ceremony, a female freshman representative goes up to the platform. Takuma Kakinouchi is shocked to see that the girl is Mayu Taneda. Just so she could be with Takuma Kakinouchi, Mayu Taneda studied extremely hard to enter the same prestigious high school. Takuma Kakinouchi has tried to avoid her, even though he loves her. When he was younger, he heard how long he would live.