Im-sol is an ordinary student who is about to graduate from college. Hiding the fact that she is a fan of Ryu Seonjae, the fifth member of the Idol group "Kamjajeon", she is living an empty life. Ryu Seonjae, a member of the Idol group "Kamjajeon", is dead! Then one day, because of an accident, Ryu Seonjae died and Im-Sol, who washing her sorrow away with a pack of soju, accidentally picked up a pocket watch and made a time leap to the past, six years ago... Gray pants, white shirt, beige knit vest. No matter how much she blinked and squinted at him, he was standing alive, right before her. “Seonjae, that’s Seonjae. Ah, it’s him. He’s real.” Ryu Seon-jae, a high school student who she only saw in the picture, was right in front of her eyes. "Ryu Seonjaeee! I really love you a lot!!" Eighteen to live again, with only one goal. It is to save Ryu Seon-jae! Im-sol’s struggling ordeal, ‘The Best of Tomorrow.’