Doom at Your Service (2021)

Tak Dong Gyeong has been working hard ever since her parents passed away. Her life seemed more stable after working as a web novel editor for 6 years, but then she gets diagnosed with glioblastoma (brain cancer). She blames her unlucky life and wishes to curse everything to disappear, which unintentionally calls Myeol Mang, Doom himself - neither human nor god - to appear. Myeol Mang says that he can grant Dong Gyeong's wishes. As her last hope, she makes a contract with Myeol Mang for a hundred days to live how she wants, risking her everything. (Source: CJ ENM; edited by unninette at MyDramaList)