My sister is Unusualy 1-12 END TH-Dub

Summary:

        High school girl Kanzaki Mitsuki "inherits" an older brother when her mother remarries a fellow divorcée with a son. Soon after, her new stepdad is transferred overseas and her mother follows him there, leaving Mitsuki to live alone with her new stepbrother, Yuya. Feeling abandoned by her mother, she stays distant from Yuya, never really getting along very well with him nor even keeping a conversation with him. One day, Mitsuki is visited by an angel/ghost named Hiyori, who takes over her body and makes sexual advances towards Yuya. Hiyori is the lost spirit of a girl who in life loved Yuya deeply, however she died before she could confess her feelings and thus can not reach the gates of heaven and obtain eternal peace.

        In order to reach heaven, Hiyori puts a chastity belt on Mitsuki that fills up every time Mitsuki has sexual feelings from Yuya, whether it be from simply going on a date with him to kissing and sex. For every time it fills up a little, Hiyori gains a step on a bridge that connects her current situation and the literal gates of heaven. If Mitsuki doesn't help her then it will result in both their deaths. If she wants to get rid of the annoying Hiyori, Mitsuki has to make some bold and sexy moves against her own brother, even if he is just a stepbrother. As the series progresses Mitsuki questions if the feelings towards her brother are of true love that goes beyond just brother and sister or if they are a result of Hiyori's feelings towards him.