Four people gathered in Naru's room for a meeting to make an adventure game. However, Chizuru who is in charge of the scenario, Mako who is in charge of music, and Emi who is in charge of the program are all dreaminging of finding the mythical creature "Tsuchinoko". So Naru's older sister Aimi says, "Why don't you make a mahjong game instead?"

However, Naru doesn't know anything about mahjong. If she doesn't know, she just has to learn, so they decided to hold a mahjong tournament, with the rule that losers must accept naughty punishment.