Recently, My Sister is Unusual

Yuya and Mitsuki have recently become brother and sister because of their parents remarrying. Mitsuki is having a hard time opening up to her new family, but their parents leave for a foreign country right after getting married before that can get any better. As Mitsuki is troubled by her new life living alone with Yuya, a amnesiac ghost girl, Hiyori, appears before her, and she is forced to help her pass on to the next world...