Jang Yumi is a secondary antagonist in the Korean Drama Boys Over Flowers. She first appears in Episode 24 where she meets a frustrated Jan Di, helping her out. They begin chatting, and after a while, Yumi comes across an injured Jun Pyo, who at first treated her poorly, but then eventually gave in to her.
Over the course of Episode 24 through 25, it is seen that Jun Pyo ends up falling in love with Yumi, who takes advantage of his amnesia by pretending to have cooked a special packed lunch that Jan Di prepared. For a certain period of time, Jun Pyo was convinced that Yumi was the person he forgot.
Yumi's intentions are revealed when, at the Gu family's mansion, Jun Pyo asks Yumi to make the packed lunch she "made" for him at the hospital. When she brings it, he is dissatisfied because he notices a difference in taste between the two lunches, and admits that he can't get Jan Di's facial expression off his mind. After saying this, Yumi turns bitter, convincing Jun Pyo that Jan Di visits him just to irritate him and that all his friends take her side.
Later, Jan Di receives an invitation to Jun Pyo's and Yumi's pool party from F4. At the pool party, Yumi reveals to Jan Di that she's in love with Jun Pyo and that he reciprocates those feelings. She then announces to the crowd that she and Jun Pyo would study abroad in America next month, which easily triggers F4.
Later in the pool party, Jan Di gives Jun Pyo's amnesia one last shot when she throws the significant J&J necklace into the seemingly deep pool and dives in to retrieve it. She sacrifices herself to Jun Pyo's amnesia, forcing the whole crowd to just watch her drown. Jun Pyo's memories come flooding back to him, and he goes to save Jan Di, forcing a bitter Yumi to walk away petulant, on the verge of crying.
She is never seen again.