Looking back at my youth, the person I least want to miss in these years has always been you. But this time, I really missed you. The film is based on the travel essay "Youth 18×2 Japan Slow Train Wandering". 18 years ago, a backpacker from Japan, Ami (Kaya Kiyohara), came to the store where high school student Jimmy (Xu Guanghan) worked, and the two worked together in the same store for a summer. Jimmy gradually developed a good impression of Ami, but Ami was going back to Japan. Faced with Jimmy who couldn't sort out his mood, Ami proposed "an agreement"... As time passed, Jimmy, who returned to his hometown, found a postcard sent by Ami from Japan 18 years ago. The memory of first love emerged, and Jimmy boarded the train to Ami's hometown and began his journey to Japan alone.