The series Samayou Midara na Lunatics (OVA) has just been announced. We think that it might be of interest to you based on your anime list.
Eifa loves her brother, Alois, but due to their status as royalty they are unable to express their love. One day Eifa was tricked and cursed by a witch seeking to become the new queen. Due to the curse Eifa can only exist at night and when it is day, her body is replaced by Alois. Their incestuous love is also exposed, and together they are banished from the kingdom.
In desperation to break the curse, Alois decides to seek the help of another witch, named Yorandel.
Adults Only (No One 17 and Under Admitted)