(R-18) Sister Princess in Isekai like world.

I always had a wish to have a sister character like those from anime, acting cute and beautiful, loving their brother, and acting with different personalities. Even so, in my former world of Earth, it was difficult to fulfill such a wish, so it was only after my death that I encountered a god who gave me the opportunity to live such a life for his amusement. As a result, after that encounter, my new life began, one that was complicated and full of new twists. I was now the heir to a family that had been cursed by the straightforward curse of not having a boy. However, a happy turn of events resulted in the birth of a boy for their family. Unfortunately, that heir was killed or ought to have passed away from overwork, and I was left to share his fate. Having a system with me! That is!