I Am Replenishing My Destiny in the Underworld

I am a temporary worker in a funeral parlor, and I accidentally get a fragmented book that can modify the deceased's "posthumous file"; every time I modify a page, I can inherit an unfinished obsession or ability of the deceased, but I will also be involved in the unsolved cause and effect of their lifetime. Later I discovered that the death records of the entire city had been written in advance...