Saki Achiga-hen: Episode of Side-A EP2 - Beginning

Kuro takes Shizuno and Ako to meet her older sister, Yuu, who she invites to become the fourth member of the mahjong club. The next day, Kuro asks her classmate, Sagimori Arata, a fan of Harue during her prime, who agrees to join the club. During Winter, Harue, whose company's manga team has since become defunct, decides to visit Achiga for old time's sake, where she is surprised to find Shizuno and the others playing. Wanting to experience the inter-high nationals once more, Harue decides to become the club's advisor. As the new year comes and the mahjong club is officially formed, the girls begin training for the prefecture preliminaries. Later, Ako encounters some of her former classmates who went on to Bansei High, who are due to become their opponents in the preliminaries.

Source: Wikipedia