Home Drama: A tragedy brings together a group of people to form a new family.
Innocent Love: The main female lead had a traumatic event happen in her childhood that affected her whole life.
Move to Heaven: The main leads are trauma cleaners so the show deals with how people met their deaths.
Semi Otoko: About a depressed woman finding meaning in her life with the help of a cicada turned human who can only live for 7 days.
Unmei ni, Nita Koi: I wouldn't call this drama sad as a whole, but there is some sadness dealing with childhood illness.
Also not an Asian drama, but if you haven't watched the Netflix series Russian Doll you should check it out. A woman who is reckless with her life keeps getting stuck in a time loop and has to solve the mystery to get back to reality.