Sung Deok-mi (Park Min-young) is a talented chief curator of Cheum Museum of Art, who also happens to have a secret: she is a fanatic fangirl of White Ocean's Cha Shi-an (ONE). In addition, she is also the fansite manager of the famous "Shi-an is My Life". Ryan Gold (Kim Jae-wook) is a standoffish artist who develops Stendhal syndrome, eventually retiring as an artist. After the current boss, Uhm So-hye (Kim Sun-young), gets investigated for embezzlement, Ryan Gold becomes the new Art Director of Cheum Museum of Art.
After rumors break out claiming Deok-mi and Shi-an are dating, Ryan suggests that he and Deok-mi pretend to date to ward off Shi-an's fans who threaten to harm her. However, Sindy (Kim Bo-ra), another fansite manager of Cha Shi-an, manages to land a job as an intern in the museum to prove that Ryan and Deok-mi are a fake couple, leaving both no choice but to continue the act even at work.
The chief curator at Cheum Museum of Art who often does not get credit for the work she does under Director Uhm, an incompetent socialite. She runs a fan website called "Shi-an is My Life" which she intends on keeping secret. She later falls in love with Ryan.
The standoffish new art director of Cheum Museum of Art who is very strict and allergic to caffeine. After seeing Lee Sol's painting, he develops Stendhal syndrome which prohibits him from painting, eventually leading to his retirement. He is also famous in New York for his perspective on new artists. He eventually finds himself falling in love with Deok-mi.
An Olympic silver medalist in judo who opens his own gym and becomes an instructor. After his single mother planned to abandon him in the hospital, Deok-mi's mother took him in and raised him with Deok-mi, who views him as family. After learning about Deok-mi's fake relationship with Ryan, he realises that he is in love with her.
An idol of the fictitious boy group, White Ocean, and also the most popular member of the group. He adores the fansite "Shi-an is My Life" stating that it is the only fansite who seems to understand him. He is a fan of artist Lee Sol and plans on collecting all of her nine paintings.
Deok-mi's father who is a quiet, soft-spoken man who began collecting suiseki stones after his business failed. Although he has few loud outbursts, he is often shown to be completely immersed in taking care of his rocks which annoys his wife.
Deok-mi's mother who is a knitting-obsessed woman who is often portrayed as a head of the household. She urges Deok-mi to give up being a fangirl citing that it would be difficult for her date since men would find her hobby off-putting. Not knowing Ryan and Deok-mi's relationship is fake, she becomes ecstatic and treats Ryan as her future son-in-law, inviting him for dinner and giving him side-dishes.
Deok-mi's best friend who is the owner of the fictitious CocoMoco café which Deok-mi, Ryan, and Eun-gi frequents. Just like Deok-mi, she is also a fangirl of Cha Shi-an who often voices her sadness that she can no longer be a full-time fan after becoming a mother. She also helps with the creation of Ryan and Deok-mi's fake relationship in order to help her friend. After seeing her worker, Joo-hyuk, in a concert, she becomes a fan and makes and runs a fansite for him.
A wealthy and eccentric, former art director of Cheum Museum of Art who resigned after her investigation of embezzlement and slush funds. Despite resigning, she plans on taking back her position after the investigation finishes. She remains a powerful authority in the museum after becoming the head director of TK Cultural Foundation, which funds the museum. She uses her connections to get her daughter, Sindy, a job in Cheum Museum of Art as an intern.
An investigative intern in Cheum Museum of Art and the daughter of the former art director, Uhm So-hye. She is a fan of Cha Shi-an and runs a fansite called "Sindy" where she calls out Deok-mi as Shi-an's girlfriend. After an article comes out reporting that Ryan and Deok-mi are dating, Hyo-jin uses her mother's connections to get a job in Cheum Museum of Art. She makes another site called, "CUPATCH" where she investigates the validity of Ryan and Deok-mi's relationship. Eventually, it is shown how she becomes a part of the Cheum Museum family through her determination, creativity and hard work.
A visual art director from New York who is in love with Ryan, her friend for ten years. She follows Ryan and also moves to South Korea after him. She works together with Cheum Museum of Art in collaboration with Cha Shi-an for his upcoming album and art exhibition. Feeling dejected learning about Ryan and Deok-mi's relationship, she becomes happy after Eun-gi tells her that their relationship is fake.
A chief editor of an art magazine who is also the mother of Nam Eun-gi. After having personal troubles, she lets Young-sook care for her son since he was an infant. Young-sook and Se-yeon becomes friends and have accepted that they are both the mother of Eun-gi. Although she has a good relationship with her son, he often calls her as Editor Nam and Yoon-sook as mom, which she doesn't seem to mind.