Hanamura Aiko is a skilled lawyer who specializes in divorce cases. She is a warm-hearted person who sympathizes with clients who are suffering from marital problems, but she grew up seeing her parents' discord, and has lost faith in romance and love. She dotes on her recently adopted dog, Sakura, and is enjoying her single life. Shirosaki Kai is the director of a 24-hour animal hospital who deals with life every day. He is loved by staff and patients for his good looks and skills, but he doesn't talk much about himself and keeps people away from him. A year ago, he rescued a stray dog ??that was brought to the hospital and named it "Shogun". One day, while walking Shogun, Kai meets Aiko with Sakura. At that time, the two dogs fell in love at first sight, and the destinies of the two began to change. Woo So Ha is a friendly young man from Korea who is popular wherever he goes. Woo So Ha has come to Japan with a mission and tries to get closer to Kai, and by chance, he also meets Aiko.
Love comes in all flavors. Secret Ingredient is the story of a Korean man who gives up his entire luxurious life in Seoul in search of his childhood girlfriend, someone he’s never forgotten all these years, in the hopes that she would fall in love with him, not for who they were back then or who they are now, but for what they can aspire to be: happy, fulfilled and blissfully in love with one another.
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?
