Every 100 days, Geon-jun repeats breaking up because he is disappointed in his lover's little place. Even so, there is one belief that he really wants to keep, and that is that there are stages in every relationship! "Dating from ancient times, you step on the progress step by step from 1 to 10, and when the 100th day is reached, then you have a relationship!" Contrary to Geon-jun, Jung-seok, a long-haired senior who looks very light but is well followed by people. After getting to know him, Geon-jun simply defines him as a 'unlucky senior'. On the other hand, Geon-jun, who has been with his girlfriend for 100 days, meets her with half worry and anticipation, but breaks up for the same reason. Feeling sorry for his situation, Geon-jun has a drunken one-night stand, and is sober from the unfamiliar pain he feels for the first time. I face the face of the other person who smiles at me,"Wait, is this person...??"