Recently, My Sister Is Unusual

最近、妹のようすがちょっとおかしいんだが。

After her mother remarries, Mitsuki Kanzaki ends up living alone with her new stepbrother Yuya when their parents move overseas. Her life turns strange when she is possessed by Hiyori Kotobuki, the spirit of a girl who must make Mitsuki fall for Yuya to reach Heaven's gate. To progress, Hiyori forces Mitsuki to wear a locking belt with a gauge of affection she has to keep filling, or die.