Seisai Chiryou ~Chijoku ni Nureru Hakui~

Main character wanders in the dark till he remembers he is in the hospital undergoing a treatment against a heart disease. A girl appears before him. She introduces herself as a Grim Reaper coming to take his soul. Protagonist cries and demands more time to prove it's a medical error. He is given just seven days. He swears to have his revenge in this hospital.

[From vndbreview]