In The World Ends With You, the basic monetary unit is yen, ¥. The total amount of yen for the partners is shared, and allows all players of the Game to buy items in shops.
The yen is held in the Wallet. Each wallet can only hold so much yen, and in some cases that amount will be too low to buy certain items. This acts as a limitation on a Player's purchasing abilities. For example, certain items cost over 1 million ¥, and since the first wallet cannot carry that much, those items are unobtainable at that point in the game.
Obtaining yen is relatively simple. Players must discard Pins to make the yen. "Yen pins," are a group of pins used largely for this purpose. These pins have no use inside battle, and can be used for Tin Pin, shop quests, or Reaper wall requirements, but are mainly discarded for the amount of money denoted by their name. For example, a "10000 Yen" pin can be discarded to put ¥10000 into the wallet. Yen pins can be evolved by trading in other pins and using them in battle. Yen pins gain PP the same way normal combat pins gain PP, and evolve in the same manner. The pins can evolve from either BPP, MPP, or SDPP. Each of these give the pin the potential to change and become a pin that is worth more. Some shop quests require specific yen pins; certain items, Books, and Swag are only available in this manner.
There is another way to obtain yen, but it is slightly more difficult to do thanks to the requirements, and more complicated. After receiving the phone menu's "Friends" and "Mingle" modes, players can set up their own "shop". This shop will show up under the friends list of any other player that they Mingle with. If a player buys something from another player's shop, then the next time that the two players Mingle, the friend who had their shop bought from will receive half the yen spent by the other player.
For example, if Joe and Max both have the game, and Joe and Max Mingle, then their shops will be open to one another. If Joe buys something from Max's shop, the next time the two Mingle, Max will receive half the yen Joe spent.