Ri-na gets a pair of underwear from her boyfriend Geun-ho, but she finds it too different in size. While waiting for Geun-ho in front of his house, she finds Geun-ho and sneaks into the house with Yoo-min and witnesses a hardcore relationship between the two. Ri-na is shocked by Geun-ho's 180-degree change from her, but she later finds out that it was his twin brother Jae-ho, and not Geun-ho. However, Ri-na, who imagined a hardcore relationship, heard the surprising news from Yoo-min that Jae-ho...