Asobitagari no Kiryuu-san

The "board game manga" is about a speed-running solo gamer and a girl who loves board games.

Sayaka Kiryuu is a model student, but rumors are going around that she is hanging out with adults. Her classmate Takuya Takatsuki ends up going with her one day, and finds out that what she does with adults is board games.

(Source: Anime News Network)