Extraordinary You (2019)

Eun Dan-oh is a high school student at a prestigious academy who suffers from a terminal heart condition. One day, she discovers a shocking truth: she and everyone else in her world are actually minor characters in a fantasy comic book called Secret. Worse yet, her character is only a plot device destined to die soon. Refusing to accept this predetermined fate, Dan-oh decides to forge her own destiny, find her own true love, and rewrite her story with the help of a nameless background student she names Ha-ru.