Engaged to the Unidentified

Mikakunin de Shinkokei is a four-panel manga based on a young girl who learns that she has a fiance, and, very soon after, ends up taking care of him, his little sister, and her own sister as they all live together. An anime adaptation is set to air Winter 2014.

Plot
Kobeni Yonomori is an ordinary girl just starting high school. Nothing unusual happens to her until her 16th birthday when she learns that she is betrothed to Hakuya Mitsumine, a boy the same age as her. Hakuya moves in from the countryside with his little sister and Kobeni's sister-in-law Mashiro Mitsumine and the two start living with her. Not to mention, Kobeni has a sister named Benio Yonomori who is two years older already living with her.

The story revolves around these four people as they try to figure out their roles in each other's lives!