Gokigenyou, Ikkyoku Ikaga?

Sae, a high school girl who has trouble fitting in at the fancy "ojou-sama" private school, has a daily routine of playing mahjong on an app by herself during lunch break. She was playing in secret, thinking that such a hobby is unfashionable...? But one day, Chisei, the most popular girl in class, finds out about it! The two girls with opposite personalities, who normally wouldn't have anything in common, become playmates through mahjong...?

(Source: Nico Nico Seiga, translated)