Furniture designer Kim Woo-jin has a secret: every day when he wakes up, he becomes a completely different person in age, nationality, and gender from the day before. Sometimes he is young and handsome, and sometimes he is old and frail. How can he fall in love like this? Fate arranges him to meet Lee Soo (Han Hyo-joo), a beautiful girl with similar interests. In his mysterious life, the only thing that remains unchanged is Lee Soo's love for him. But their love also faces new tests every time Woo-jin "transforms".