Woo Hyun is a Korean man, and Haruka is a Japanese woman. They live different lives, but they both carry emotional scars from their first love. While looking for answers and hope, their fateful encounter will change their lives. It started with one message… Haruka, a stage actress in Seoul, has been in a slump ever since she broke up with her first love. She cannot forget him and keeps sending messages that go unread on LINE. Despite her emotional hurt, Haruka wants to believe in love. In Tokyo, Woo Hyun, an aspiring movie director, keeps on doing interviews concerning “love”. After being deeply hurt by his girlfriend, who thought about getting married, he no longer believes in love. Haruka and Woo Hyun have both grown timid of love. The two of them, who live apart in Tokyo and Seoul, have a chance encounter because of a LINE message delivered to Woo Hyun’s smartphone from Haruka. They exchange messages without knowing each other’s faces and are drawn to each other before they realise it
Hitomi, a Japanese resident, comes to Hong Kong after the death of her fiancé Tatsuya in a fatal accident to settle several important matters surrounding his demise. Although the incident was years ago, it has apparently left an indelible mark in her life as she could not forget him. Kar Bo, an undercover cop, was involved in a drug bust-up which would later incriminate him. Hitomi stumbles into him and was amazed that he looked remarkably similar to her dead lover. Although Hitomi was conscious that Kar Bo can never be the real Tatsuya, she endures his hardships with him unfailingly which results to having strong feelings for each other.
Ami, a backpacker from Japan who is four years older than high school student Jimmy, shows up at his part-time job. The two end up spending the summer working at the same store, but Jimmy gradually develops a faint crush on Ami. The two of them grew closer as they rode motorcycles together at night and went to the movies, but suddenly, Ami decided to return to Japan. Ami proposes her "one promise" to Jimmy, who can't sort out his feelings. As time passes, Jimmy visits his parents' house for the first time in a while and finds a postcard that Ami sent him 18 years ago when she returned to Japan. Jimmy's memories of his first love come back to him, and he takes his first solo trip to Japan to confront his past and examine his present. Jimmy rides the train while listening to songs that remind him of his memories with Ami, and he heads to her hometown. Will Jimmy be able to reunite with Ami?
