Mikakunin de Shinkoukei

The story is about an ordinary girl named Yonomori Kobeni who suddenly heard that she is betrothed to a boy named Mitsumine Hakuya. Somehow Hakuya moved in from the countryside and started to live with her, bringing his younger sister with him. Added Kobeni's elder sister who already lives with Kobeni and is crazy about her, the story revolves around these four people and their identities as "couple" and "family."