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?
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?
Left alone on a trip to Hong Kong, Tomoko, a sales woman from Japan finds herself the victim of a purse-snatching. The police arrest the man she points out, but it turns out to be the wrong person: a young Korean man named Ji Hoon. Despite his anger and humiliation, he takes her out to dinner since she has lost all her money, and in return, she agrees to model for his amateur film. What follows is a magical and romantic two days. Upon returning to their respective countries, Tomoko must return to her nine-to-five job and Ji Hoon must resume studying to join the family business rather than pursuing his dream of becoming a film director. But soon the two begin to email each other and rekindle their relationship despite the distance and obstacles between them. Marking the very first time in television history that a drama has been co-produced between Japan and South Korea, the story shows us that love has no borders.
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
Kawakubo Ryo is a detective on a special team. When he was a child, he lived through a difficult time. He lived in poverty and his mother's negligence led to his younger sibling's death. His mother went missing and he has been looking for her. Song Shi-On is a smart guy. He graduated from a top medical school in the United States. He happily spends time with his girlfriend, but an experiment on his brain causes him to lose his memory. Kawakubo Ryo and Song Shi-On have nothing in common but work together on a special team formed by a secret organization of police officers. They try to solve difficult cases.
