SHOUBUSHI DENSETSU TETSUYA

In the year 1947, the people of Shinjuku are down on their luck. With little money to buy food or necessities, some resort to gambling in order to survive. Traveling Tetsuya chooses to spend his time at Mahjong parlors where he is wiping the floor clean with his adversaries. However, when Tetsuya meets the intensely skilled Boushu-san, he realizes that his skills are still lacking. (Source: Anime News Network) — Description from AniList community (anilist.co).