Almost tempted to put tragedy of a long age, but it seems like theres no regrets and reimu and yukari can still freely meet in the afterlife.
I mean does it count if it seems like they died of a disease rather than old age.
Edit: decided to add this to tragedy of long life because posts like post #502068 show that they don't have to be of old age and posts like post #777099 show that they don't have to be depressing.