Money is the currency Urotsuki can collect in her dreams, represented by the kanji 夢(Yume, Dream).
Once per dream, the piggy bank in the dream version of Urotsuki's Room will give you money equal to the percentage of maps you've visited.
Killing NPCs can sometimes yield 100夢 (1/8 chance). The NPCs in Ecstasy World seem to give out money more often than NPCs in other areas, making this a good place to get money quickly. Killing the blue boy in Urotsuki's Dream Apartments always yields 50夢.
The Mysterious Maid will give you 500夢 when you interact with her for the first time.
There is a smiling green blob in Graveyard World near the sculpture room that will give you 5000夢 if you can chainsaw it. However, doing so is very difficult, as it moves around very quickly.
If your money is below 500夢, you can find 100夢 by checking the Box Shop Keeper's drawers in Japan Town and going into the gap in the hedges near the Underground Bar.
Once per game, Urotsuki can receive money from a customer in the hotel.
Money can also be gambled at the kura slot machine minigame in the Developer Room for profit or loss, at 100夢 per spin.
There are currently only a handful of things Urotsuki can spend money on. The many vending machines found throughout the dream world are the easiest to access. Urotsuki may purchase drinks from them for 100夢.
Urotsuki can also buy alcoholic drinks (200夢 per drink) at the Underground Bar in Japan Town. Drinking too much may lead to interesting results.
Masks can be purchased from the shopkeeper in the Mask Shop for 500夢 each. These get cheaper by 10夢 with each purchase, to a minimum cost of 100夢 per mask.
Urotsuki can also lose money. The vending machine in Mushroom World, for example, will steal your money and not give you a drink. A sane clown (nicknamed Pennywise) in the gray building of Guts World will also steal some money from you if you try to kill him.