Omae Imouto Janakute Iinazuke Datta no ka yo!?

Synopsis

Humanity, love our little sister. I miss the time when her younger sister Kana was fond of me. Takashi Shiina lamented the current days when he was often ignored. One day, his parents cut out a shocking story. Surprisingly, he wasn’t his real son but he was his sister Kana’s fiancée?