改編自在台灣掀起話題的網路遊記「青春18×2 日本慢車流浪記」
「亞洲公共財」 許光漢 ╳ 最具潛力的新生代 清原果耶

劇情緣起於18年前的台灣，追溯初戀的旅行從此開始，高中生Jimmy（許光漢 飾演）打工的地方出現了一位大他四歲、從日本來的背包客女孩Ami（清原果耶 飾演）。兩人夏天一起打工，漸漸地Jimmy對Ami萌生純純的愛意。就在距離越來越近的時候，Ami突然要回日本。看著難以接受的Jimmy，Ami提出了「某個約定」。時光飛逝，Jimmy回到久未進門的老家，在房間內找到18年前Ami從日本寄來的明信片。初戀的記憶湧上心頭，決定展開第一次在日本的單人旅行。Jimmy聽著和Ami有共通回憶的歌曲，坐火車前往她的故鄉。究竟Jimmy和Ami能夠再次相遇嗎？

Jimmy goes back to his parents' house for the first time in a long time and finds a postcard from Ami.
Ami, a backpacker from Japan, showed up at the his work place 18 years ago. Jimmy's memories of his first love come back to him, and he sets off on his first solo trip to Japan to face the past and look at the present. As he rides a train listening to the songs they heard together, he heads for her hometown. Will Jimmy be able to reunite with Ami?