The Laughing Salesman S03 E08 Private Tutor

Yokomichi Yukio is concerned about his son Manabu's academic ability, and Moguro sends in a tutor who teaches Manabu to play and have fun. Manabu's grades improve and Yukio agrees to him joining a mahjong game with his friends and Manabu wins. However Manabu is so successful, he then becomes a professional mahjong player.