Iinazuke (許嫁は妹さま！) br Shun lives alone with his sister Yuna after their father remarries. Yuna acts harshly to Shun and often yells at him for the slightest mistakes. Suddenly Haruka arrives unannounced and claims to be Shun and Yuna's new sister. Since she's Shun's new sister she believes that must mean they love each other and if they love each other that must mean they're engaged to be married and if they're engaged to be married that must mean they should do ecchi things together.