Oneechan ga Kita  

My Big Sister Arrived, お姉ちゃんが来た

The narrative centers on 13-year-old Tomoya Mizuhara who experiences a significant change in his life when his father remarries and he gains a new sister, Ichika. She is an older teenager with somewhat peculiar behavior, and her affinity towards Tomoya can be intense at times. Additionally, Ichika's friend Ruri enjoys inflicting pain on others, while Marina, another of Ichikas friends, has large breasts and is half-Japanese.