Based on the internet novel of the same title and written by Guiyeoni, Do Re Mi Fa So La Ti Do is a touching love story with bittersweet elements. Jung-won wears a funny dragon suit, while working at the amusement park, and pours soda on Eun-gyu, because of his taunts. A short while later, Jung-won finds out that Eun-gyu has moved into the house next to hers. Eun-gyu now threatens to tell Jung-won’s parents that she works part time at a local mart. To keep Eun-gyu quiet, Jung-won agrees to carry his guitar for a week.

Jung-won then starts to develop feelings for Eun-gyu, who is the lead singer of a band called Do Re Mi Fa So La Ti Do. Eun-gyu also starts to develop similar feelings for Jung-won. The two soon become a couple. With an odd twist of fate, Jung-won went to the band’s rehearsal room and meets a familiar person from her past, a boy named Hee-won. Their relationship makes everything more complicated. 10 years ago, Jung-won and Hee-won were close friends, but because of a personal matter, they stopped talking to each other completely. Jung-won is now surprised to learn that her ex-close friend is now best friends with her boyfriend. Hee-won admits that he still likes his best friend and he wants her back. Now Jung-won is torn between her friendship with He-won and her love of Eun-gyu.