Nam WooHyun goes to celebrate his graduation with friends at a beach in JeJu. There he is able to meet with Shi MinJoo who stealthily refers to herself as Gi MinSeo (you, older twin sister). WooHyun and MinJoo profoundly have a relationship as Woohyun is unaware that MinJoo sees this love as only fun and games, opposite of WooHyun who is extremely serious about this first love and promises her that "in this life, he will absolutely refuse to get married if his bride is not the women named Gi MinSeo."

Woohyun asks MinJoo to wait for him to work and prove his love in order to get married together, but she quietly disappears, leaving no trace. WooHyun goes out to search for her in every way without knowing that while he is anxiously concerned about her, MinJoo returns to make love to new men after another and gets wildy dead drunk.

Time passes by and WooHyun is exceedingly happy when he is able to find MinSeo (the real one, you) at a banquet, but WooHyun must meet with disappointment at the time MinSeo (you) say that you have never met him before. Though WooHyun tries to revive the relationship, he gets slapped in the face with anger because you think he is looking down at you. WooHyun "loves" and is angry with you, "understanding" that MinSeo (you) dislikes the fact that he is not rich. WooHyun goes back home with sorrow and tells everything to DanBi, his mother. DanBi tells her son that it is good that he knows MinSeo's loss before WooHyun becomes rich because at this moment, WooHyun receives inheritence of billions of dollars from his grandfather who just passed away.

While MinJoo still commits identity theft using the name MinSeo to deceive men that she has a relationship with, she finds love with JeongWeon, a womanizer who just playfully hooks up with MinJoo and languidly leaves her. MinJoo is furious and hurt and blames that her life has to be like this because of her father who refused to raise her like MinSeo (you) without heedlessly knowing that MinSeo (you) also has to meet with hardship as you have to live with YooRi, your stepmother who often awaits to make fun of you constantly with words. MinSeo (you) has to go out to find a job and unexpectedly it is the company that WooHyun is the president of. WooHyun is glad and takes the opportunity to get even with MinSeo (you) in various ways because of a misunderstanding. It gets worst when JeongWeon works as an accountant at the company and insults MinSeo (you). WooHyun asks JeongWeon who therefore tells the "truth" that he has a deep relationship with MinSeo. This causes WooHyun to understand that MinSeo is a women who sees love as only a game.

JeongWeon watches and observes MinSeo's (your) behavior until he knows that truthfully MinSeo is a different person from MinJoo and tries to hook up with MinSeo (you) with his womanizing nature. This makes WooHyun believe more that you had a relationship with JeongWeon before. WooHyun thinks about taking vengence on MinSeo (you) who "looks down at his sincere love." He then pretends to be good to cause MinSeo (you) to fall in love with WooHyun unconsiously and it is the same time that MinSeo's household is a mess because YooRi is secretly addicted to gambling and makes SaeJin, MinSeo's (your) father, to become ill. MinSeo (you) then asks for help from WooHyun. WooHyun gives his word, but has a condition that you have to marry him. MinSeo (you) have to throw away your dignity for you to help your family.

When MinSeo (you) become WooHyun's wife, you have to meet with a cold war that people in the house throw at you. MinSeo (you) is upset and offended that everyone does not see you as the wife or in-law at all. As for MinJoo, when she sees the news of MyunSoo and MinSeo's wedding, she is shocked that she now knows that he is rich and WooHyun had to get married because he misunderstood that MinSeo (you) is actually her. Greed and fury make her decide to go see WooHyun and make up a story to trick him that she is still adhere to their love and promise. WooHyun very much feels sorry for MinJoo and hates MinSeo (you) more that you deceived him. 

WooHyun brings MinJoo to meet MinSeo (you). MinSeo (you) is very startled to know that MinJoo is your younger twin sister. MinJoo feigns to be good in front of MinSeo (you), but behind WooHyun, MinJoo severely abuses her older sister who "snatched" WooHyun away from her and demands for you to give WooHyun back. MinSeo (you) consequently decides to leave WooHyun. This causes WooHyun to understand more that MinSeo (you) never had a heart for him at all. WooHyun is sad, but pretends as if he is relieved that everything ended without trouble; however, when he finds out that MinJoo really stole MinSeo's identity, WooHyun goes back to feeling strange. He is just aware that his bond with the real MinSeo (you) is lost.

How will the love between WooHyun and MinSeo (you) end up?