Im-sol is an ordinary student who is about to graduate from college. Hiding the fact that she is a fan of Ryu Seon-jae, the fifth member of the Idol group ‘Potato Pancakes’, Right now, she is doing cosplay in public. -BREAKING NEWS- Ryu Seon-jae, a member of the Idol group, ‘Potato Pancakes’, is dead! Then one day, because of an accident, Ryu Seon-jae died and Im-Sol, who was in sorrow, 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. “Seon-jae, that’s Seon-jae. 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. This may be an opportunity. An opportunity to prevent Ryu Seon-jae from joining Potato Pancakes and becoming its 5th ‘unlucky’ member. An opportunity to save Ryu Seon-jae, who died at the age of 23 with no luck because he took a wrong cold medicine. Eighteen to live again, with only one goal. It is to save Ryu Seon-jae! To save the best in the past, Im-sol’s struggling ordeal, ‘The Best of Tomorrow.’