夢子が百花王学園に転校する1年前。ごく普通の家庭に生まれた少女、早乙女芽亜里は転校試験に合格し、百花王学園に入学する。しかし、彼女が入学を期待していた学園には、「賭博洗礼」という奇妙な校則があった。夢子を「双子」としてペアを組まされた芽亜里の賭博狂生活が幕を開ける！
It's a year before Yumeko transferred to Hyakkaou Academy. Saotome Meari, a young girl who was born into a very ordinary family, passed her transfer examinations, and has started to attend Hyakkaou. However, the school she expected to attend has a crazy law, the Baptism of Gambling. Paired with Yumeko as her "twin," the curtain opens on Meari's gambling mania!
