Choi Yeonjun is a high school student. Choi Beomgyu suffers from the mysterious ailment "Blue Hour disease." People who have the disease show a faint sparkle under the blue hour and the sparkle gets brighter as their death gets closer. Beomgyu is not allowed out of the hospital and he will not live long enough to become an adult. Yeonjun offers to help him carry out his wishes before he passes away.