Tsukishima Shun, born in Kyoto, experienced bereavement at the age of nine. He had no choice but to move to Nagano to stay with his aunt, and so he was separated from his childhood friend, Sasaki Yui. They promised each other that when they reunite, they will get married to each other. One day, Shun moved to Tokyo with his aunt. There, Shun got into Shirohana High School in his first year of high school. Unexpectedly, he met someone that seemed familiar to him...