Aria is going to attend a vocational school in Tokyo. She has no money and is not good at part-time work. She came to Tokyo asking if she could stay in her brother's room for a while. Her younger sister is a plain, unemployed country girl. The brother decides to do something about it, and in order to help his sister grow up, he makes her wear cute miniskirts and naughty underwear. Once she's changed, her younger sister is unrecognizable... naughty and erotic... and he can't help but end up training her in a naughty way!