I found an easy way to make money while afk on PC. This is really useful if you are trying to get all the completion points or if you are just trying to ball out. There is also an achievement for getting 10,000,000 yen.
Basically, you want to go somewhere where enemies don’t spawn (Purgatory, Gambling hall, etc). After that you will want to put on the Ebisu socks and key bind walk to left mouse button. Go to a corner or wall and turn on an auto-clicker. Boom big money, It averages more than 100,000 per minute of auto-clicker.
P.S. if the frequency of the auto-clicker is too high, it may not work. To fix that, lower your click speed.
How to make quick money
Video tutorial.