Someya's Mahjong Parlor is a maid mahjong parlor run by Mako Someya's grandfather. Mako helps out whenever she can. At the parlor, some rules include that it's the employee's job to play with the customer when they aren't enough players at the table and they play "no rate" so no one has to worry about losing. Yasuko Fujita is a regular customer here and loves the katsudon. Hisa Takei sends Nodoka Haramura and Saki Miyanaga here to get humiliated by Yasuko and learn that they need to improve their games before the prefectural tournament.
Differences in Anime and Manga
In the manga Mako's grandpa runs a maid mahjong parlor. However in the anime, he runs a maid cafe that has a mahjong table in the corner. It is later stated that he use to run a mahjong parlor before turning it into a cafe.