“Yin? Si: If you are not sinister, how can you survive? If you do not command, what makes you a god? The Book of Yin’s Command lays out the world’s darkest forces, adapting the Thirty-Six Stratagems into tens of thousands of schemes and stratagems. So even in a cultivation world rife with deceit and conspiracy, you must row against the current and press on steadily, until you can finally stroll with ease! ... One stroke once severed yin from yang; one stroke will divide life from death. One book once rivaled a fortune in gold; one book seeks to turn the boundless seas upside down. One person stands alone, while the book is always by his side!”
It's a fantasy novel! It has little to do with the underworld!