This drama is a diary of Hyeonsu and Seungyeon 10 years ago, who have become 30 now. Because of trivial misunderstandings and different memories, they feel bitter as it feels like that the expiration date of their first love has ended. But the diary is covered with bright colors of their youth and that spring with heart-throbbing first love. Would this make their tomorrow a bit lighter? We want to share this story to every tired Hyeonsu and Seungyeon of this world.