Touhou Unreal Mahjong uses standard riichi Mahjong rules, with slight variations for each of the game's stages. In addition, each of the game's characters has a special ability outside of the standard rules of the game.
In the game's story mode the player faces three sets of three set opponents, with dialogue before each match. To continue you must place third or better in the first match, second or better in the second match, and first in the final match. Upon beating the third match, the next character's story mode will be unlocked for play. Additionally, those characters you faced in story mode will be unlocked for use in freeplay.

There's also a freeplay mode in which the player can choose any character to play. A player may use any number of duplicate characters. Additionally, there is a netplay option which requires a serial key to unlock.

An extra stage can be unlocked through story mode.