You weren't my sister, but my fiancée!?

<p>Humanity, love your little sister.<br/><br/>I miss the time when her younger sister Kana was fond of me.<br/>Takashi Shiina lamented the current days when he was often ignored.<br/>One day, his parents cut out a shocking story.<br/>Surprisingly, he wasn't his real son... but he was his sister Kana's fiancée! ?<br/><br/>The definitive version of Reiwa's younger sister manga!</p>