In the romantic comedy, quiet Japanese security guard Kohei Namiki (Hidetoshi Nishijima), whose only real interest seems to be astronomy, is ordered to bodyguard top Korean actress Han Yoo-Na (Kim Tae-hee) at an exceptional production set in Japan.
Namiki is a single man approaching his 40’s. He works at security company as a part-time job. He also has a sweet and handsome appearance, which some people take advantage of. Kohei is easily swayed by those around him. Kohei often takes care of his sister’s three kids because Kohei’s sister has a habit of wandering around, but he is a passionate man and dreams of finding his star. Because of his family and economic situations, Kohei can’t follow through on those dreams.
One day, Kohei is assigned security detail for the beautiful actress Han Yoo-Na (Kim Tae-Hee). Yoo-Na has a pure and kind spirit. Even though she has a near perfect appearance and style, she prefers to act like normal people. She enjoys eating simple Japanese foods and on the filming set Yoo-Na will stop to help others. She seems to be the envy of all, but really feels the loneliness of an idol of the entertainment industry, and she also has a sad secret.
At first, bodyguard Kohei and top star Yoo-Na don’t get along. Over the next 99 days their relationship changes, with the deadline of the 100th day when the contract ends.