The pure love in high school, which lasted for ten years, has been constantly changing, from heartbreak and quarrels to the pain of broken love and falling in love again, and they are entangled repeatedly. This is a love story between a "pure man" (played by Kim Young-kwang) who only has eyes for one woman, and a "first love girl" (played by Park Bo-young) whose inner thoughts are hard to guess. The ups and downs of love are about to unfold...