Park Yun Jae is a university student studying astronomy. He met Kim Ji Eun on his first blind date while attending university. They fell in love and became boyfriend and girlfriend. One day, a strange man appears in front of Yun Jae and tells him that he is Ji Eun.
Ji Eun is a pretty and warm-hearted woman. One day, she wakes up and finds herself changed to a man. She explains the situation to her boyfriend, Park Yun Jae. She begins to use the name Kim Ji Hun and learns how to live as a man from Yun Jae. The two decide not to 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, popular girl Kang Min Ju is attending the same university as Yun Jae and has a crush on him.
(Source: AsianWiki; edited by MyDramaList)