When a new girl group is set to debut one of the members named Jacky breaks her foot during practice. Jacky calls her twin brother Kai to take her to the hospital and finds out her ankle is in a really bad condition. To not set back the debut stage Jacky asks her brother to fill in for her until she gets better. Kai being the caring brother he is, dresses up as his sister and preforms as a girl. He soon gets close with the members especially one who's name is Hyomin. They get close and he soon starts to have feelings for her, but is scared to hurt her if she finds out he's a boy.