Engaged to the Unidentified

This is a four-panel comedy manga about Kobeni Yonomori, who on her 16th birthday suddenly has a young man with little presence named Hakuya Mitsumine and his little sister Mashiro appear in front of her. It turns out that Hakuya is her fiancé, and Mashiro is her future sister-in-law. The three (and Kobeni's big sister Benio) start living together underneath the same roof, and hilarious happenings occur.