Koshigaya Girls' High School

Koshigaya Girls' High School, located in Saitama Prefecture, is a national tournament rival of Achiga Girls' Academy in the spin-off manga Saki Achiga-hen episode of side-A and its anime adaptation. Koshigaya makes a small cameo watching the side B semi-finals.

History
Koshigaya had never advanced into the second round in its previous four appearances in the Inter High. They finally advanced to the second round during the 71st Inter High School Mahjong Championships. However, they did not advance past this round, losing to Achiga and Senriyama.

Roster

 * Girls' team tournament
 * Sophia Arai (vanguard)
 * Hanako Asami (sergeant)
 * Shiori Mizumura (lieutenant)
 * Tamago Utsugi (vice captain)
 * Keiko Yagihara (captain)