You're On Fire, Pen-chan

Watanabe Yuuichi, also known as Pen, is a man who loves mahjong with all his heart. His innocent way of life makes everyone around him passionate, and they become his followers. This is a story of how Pen grows as a human being by getting involved with several people, including Yamazaki, a yakuza who notices that he enjoys playing mahjong even if he loses.