DR2 Night Janki

DR² Night Janki is a mahjong game with adult scenes. The game has two modes: "Story" and "Regular". The story mode is set in a medieval castle, which is said to be ancient grounds for sorcery, but is currently controlled by the mysterious Rumira, who runs a mahjong club. The hero, a man named Ryuuji, decides to investigate the castle, and therefore has to defeat its inhabitants (all pretty young girls) in mahjong matches.

[From Mobygames]