MOON-017 I became a fuck buddy with the part-time sister who works at the mahjong parlor and kept fucking her all night long, cumming inside her four concealed kanji

An, a slender older sister who works at a mahjong parlor. One day, a woman plays mahjong with a man who was brought to a mahjong parlor for the first time by her boss. A man is attracted to her kindness and starts going to her, and the relationship gradually develops into an adult one. After playing mahjong with their clothes off, the two end up touching each other again and again until morning. What will happen to their love affair, which is like a game of mahjong?