Mikumo and Sei have been friends ever since they were kids. They were so close that people would think they were a couple in middle school. Due to her parents job, she had no choice but to move with them to China and thus the two of them parted ways. He gave her his hat as a parting gift but she didn't get the clue behind it. A few years later, she returned to japan and reunited with him in high school. Will their first love reunite once again?