Woo-jin finds himself with a girl in bed the very morning. His body is twice the size of yesterday's figure. Before she wakes up and finds out that she slept with someone else, he moves from there, unknowingly, to her. Yes, every day Woo-jin wakes up in a new human body. Additionally, he needs to get used to the fact that he is a different person every morning. He must get used to his new voice, eyesight, and body. He can sometimes be a man or a woman, young, old, or alien. Woo-jin has created a system where he has a variety of shoes and clothes to accommodate every body type and, of course, various toiletries depending on whether he is male or female, after years of transforming into different persons. In addition, he has a Brannock foot measuring gadget to measure his feet and a phoropter to test his vision so he can select the appropriate size of shoes.
Woo-jin, currently a furniture designer, has never woken up in the same body twice, regardless of age, gender, or nationality. Song-beck, his closest friend, works with him, handling sales and visiting Woo-jin's clients in person. He runs ALX, a furniture firm that specializes in creating custom-made furniture for each of its clients. Just because of his friend, he visits the night bar often and goes as usual, running before the girl wakes and before she gets to know with whom she slept. Woo-jin uses his computer to videotape himself every morning so he can see who he is that day. It takes some getting used to seeing a different visage in the mirror every morning. This started happening 12 years ago.
On his eighteenth birthday, Woo-jin wakes up one fateful day to find that his body and face are not his own. She is equally shocked when he confronts his mother about his new look. He cries, and she accepts him for who he is. He is quite shocked and puzzled. Woo-jin can manage his unusual condition with the support of his mother and closest friend. When Song-beck came to know about this for the first time, he even made Woo-jin feel lighter for who he was. Woo-jin can work in his home and keep his secret from others because he designs furniture. When they learned that other companies were copying his design, Woo-jin decided to design custom furniture for everyone.
One day, Woo-jin starts to have feelings for Yi-soo, a worker at a furniture business. He starts going to see her every day and even strikes up a conversation with her, but she is unaware of this because he appears to be a different person every day. He waits to ultimately approach her and ask her out on a date until the ideal moment when he turns someone handsome. He wants to keep seeing her as the same person. Finally, he is successful in asking her out. After their successful first date, they plan to go on a date the next day too. He thus goes without sleep in an attempt to maintain his identity as the guy who went out with Yi-soo at first. He made it to their second date without any changes occurring in his body. Sleep deprivation eventually occurs on the third day and causes him to lose his body, and he chooses to quit talking to Yi-soo because he does not want to tell her his secret.
Yi-soo gets perplexed, knowing nothing about why he refused to catch up for breakfast. When Woo-jin starts working as a temporary intern there, the female Woo-jin invites her to supper. Despite her misgivings, she follows the female Woo-Jin to his house again, where he reveals her identity and shows her recorded videos of herself every morning. But Yi-soo is so confused and not ready to accept whatever Woo-jin is up to. Yi-soo thinks that she has been betrayed.
Yi-soo keeps on thinking about the same thing that Woo-jin said, and to make it clear, she visits Woo-jin (who is in his female version) at his house. Yi-soo says that she wants to sleep with him tonight and to check whether he is changing into a different person or not. And this female Woo-jin doesn’t speak Korean. Depending on the day, he can even speak in multiple languages. On the inside, he remains the same, yet on the outside, he constantly changes. She is taken aback, and it takes her some time to understand and come to terms with Woo-jin's true nature. Yi-soo is surprised to see Woo-jin as a different person the next day.
Every time Woo-jin changes, they stay together and make plans to come back together. He even changed into a kid, and still, she enjoyed their company. Since he changes into a different person every day, they make sure that she will recognize Woo-jin as soon as he grips Yi-soo's hand in such a way. Woo-jin takes Yi-soo to meet his friend Song-beck. He turned once into an old woman when Yi-soo was supposed to bring her to the company’s party. He still struggled so hard to become a different person and entered as a handsome man at her company party. Every day, they recorded video of both of them in Woo-jin’s laptop. Soon, Woo-jin takes Yi-soo to meet his mom in her shop. At dinner, her colleagues asked Yi-soo to bring her boyfriend to join them since they felt he was different looking at him the second time. Yi-soo tells them to bring him the next time.
After a while, Yi-soo begins to have relationship problems. One day, in a playful way, Woo-jin asked Yi-soo to find him among the crowd. After a few minutes, he just came and folded her hands, saying nothing. She had to have complete faith that the stranger taking her hand was Woo-jin since she could never really know who he was or what he would look like. Woo-jin convinces her within the same night. Woo-jin makes a ring for Yi-soo to propose to her. Yi-soo is the subject of gossip, with others speculating that she is dating various men every time. She eventually reaches a breaking point, as a result of which she needs medication to manage her stress, worry, and sleeplessness. Woo-jin proposes to her, and she is not so happy about that. Yi-soo expresses that he is only about himself, not her. She says when he needs time to wake up every morning and get himself ready for the look, she needs time too.
And she also mentions that it's not easy to convince the family. Yi-soo, at her therapy with the doctor, says, “When I look at him holding my hand, a stranger is smiling at me. When he touches me, I keep telling myself that it’s him, the man that I love, but I still can’t be sure. I try to feel him with my eyes closed. Think I am going crazy.” Yi-soo also mentions, “He won’t survive without me.” After taking too many pills, she gets admitted to the hospital. Woo-jin thinks he is the reason for her state. Worried Woo-jin meets his mother and gets to know that his father abandoned them because he suffered from the same illness. She says, “When people started gossiping, I made your father leave, and he disappeared. Now, Yi-soo is suffering from the same situation as mine. Yi-soo is scared and can’t talk to anyone. When you stay away from her, she gets better, she says.” When Woo-jin learns about it, he decides to vanish from her life to assist her.
One last time, Woo-jin meets Yi-soo and has dinner together. While he walks her home, he says that they should break up, and it is their right choice. He also asks her to stop taking pills and walks away. Yi-soo worries so badly and says she remembers everything but not his face. When time passed, she turned normal and stopped taking pills. Yi-soo is adamant about finding Woo-jin and never stops loving him. The company where Yi-soo is working needs to renew its contract with ALX. So on behalf of the company, Yi-soo meets Sang-beck, who now hates her. There, Yi-soo finds the packages have arrived from the Czech Republic. Realizing her mistake, she decides to go after him.
Yi-soo is successfully locating Woo-jin again in a new nation (the Czech Republic). She doesn't care about the change or how he looks. She says that she knows him and loves the real Kim Woo-jin inside. She tells him that she still has feelings for him and that she wants to live a lifetime with him. Following this admission, Yi-soo asks Woo-jin if he will marry her, and following that, Woo-jin proposes to her with the ring he made. On the other side, Woo-jin’s mom apologizes to her husband, who recently showed up. He replies that he knows the pain that she was through and has been waiting for her from a distance. She says she knew it too and asks him to stay with her forever. And yes, it had a happy ending.
