Janji

Nako Nishino is a new kindergarten teacher. Nako's dream job as a teacher starts with a shocking turn of events, when she found herself playing mahjong against kindergarteners...! Suddenly, Nako found herself in debt for 1 million yen, and the strongest player at the school, known as "Janji", is determined to help her out.

(Source: Shonen Jump Plus, translated)