It has been quite some time since Hoozuki-san Chi no Aneki concluded, but new adventures await as (+Imouto) rejoins the hilarious pranks of her perverted stepsibling and siscon, Gorou, and his elder stepsister, Haru. Their fun is interrupted when Gorou's cousin pays a visit, causing Haru to feel threatened by the possibility of losing Gorou's unwavering commitment.