Koukou Debut Shita Juumai Ga Mount Tottekuru

I have a younger sister who's 3 years younger than me. Before, she was just a generic girl, but ever since getting into high school, she's become a wonderful gal. Going through our everyday life, she would mount me, or so I thought, but there were tears, and believing lies, huh? It's only her look that's changed!? Dominating and getting dominated! A pure older brother and a bad and easy going little sister, 1 on 1 love comedy, begins!!