Gokigen You, Ikkyoku Ikaga?

Synopsis

Sae finds it difficult to fit in at a prestigious girls' high school. During lunch break, she secretly plays mahjong on an app by herself. Until one day, Chise, the most charismatic young lady in the school, finds out about it! Will Sae be able to show her through the wonders of mahjong? (Source: Houbunsha)