This is NOT Borderline H...it is MOST DEFNIITELY H.
The synopsis is dead-on for what happens in the "story", if you can even call it a story. There's another actual anime that has the same type of premise and it's far better because it's a full series that focuses on the problematic relationships that have to be juggled by the possessor and the confusion that is had by the possessee.
As an old-school H, it's actually not bad. It's a little bit of F'd up at the end with a <spoiler alert> gangbang rape scene...but the animation is decent for the time-period. Enjoy.