Sae Kitaoji, a student at the elite all-girls Ōtori Academy, struggles to fit in after missing the first week of school due to illness. Unable to connect with her classmates, she spends her lunch breaks playing mahjong on her phone, keeping her hobby a secret out of embarrassment. One day, Chise Kannami, the most popular and charismatic girl in class, discovers Sae playing mahjong. Instead of judging her, Chise becomes intrigued and asks to learn the game. The two girls bond over mahjong as Chise takes up the hobby herself, and their friendship deepens through matches and study sessions.

The story unfolds at Ōtori Academy, a prestigious all-girls school where social expectations and refined manners dominate daily life. The mahjong games serve as a bridge between Sae’s reserved nature and Chise’s outgoing personality, allowing both characters to grow. As the girls explore the rules and strategies of mahjong, they also navigate school life, make new friends, and overcome personal insecurities. The narrative balances gentle comedy with the learning process, making the game accessible to viewers unfamiliar with mahjong. Key arcs include Sae gaining confidence through teaching and Chise discovering a passion that challenges her privileged worldview, ultimately highlighting how a shared interest can forge a genuine connection.