Park Yoon-Jae (Yoon San-Ha) is a university student studying astronomy. He met Kim Ji-Eun (Arin) on his first blind date, while attending the university. He fell in love with her and they became boyfriend and girlfriend. One day, a strange man appears in front of Park Yoon-Jae and tells him that he is Kim Ji-Eun.
Kim Ji-Eun is pretty and a warm-hearted woman. One day, she wakes up and finds herself changed to a man. She meets her boyfriend Park Yoon-Jae and explains her situation to him. She begins to use the male name Kim Ji-Hoon (Yoo Jung-Hoo) and learns how to live as a man from her boyfriend. Kim Ji-Eun and Park Yoon-Jae decide to not break up and to wait for her to return to her original female appearance to continue their relationship. They try to figure out a way to make that happen.
Meanwhile, Kang Min-Joo (Chuu) is a popular girl attending the same university as Park Yoon-Jae. She also has a crush on him.
