Hiroko Murohashi is a third-year student at Takatoobara Middle School in Nagano Prefecture. She is a former teammate of Nodoka Haramura and Yuuki Kataoka in the previous year's prefectural middle school mahjong tournament. Because she is often seen together with younger teammate Maho Yumeno, Yuuki calls them the "Muro-Maho Combination."

In the first anime series, the Hiroko and Maho attend Nagano's prefectural high school tournament to see Nodoka's final match. In the manga, the two do not attend and are instead invited by Hisa Takei to Kiyosumi High School's national tournament training camp.