Fantasy: I Became the Villain in the Book

He traveled to the fantasy world in the book and became a villain. The son of destiny is about to show off and slap him in the face? Just kidding. Grandpa is the founding marshal of a fantasy country and the king of the opposite sex. My father and second uncle are both generals who hold military power. The mother is the eldest princess and owns the richest bank. I am the only male of three generations in my family, and I know all the tricks in the book. It's not easy to trample to death a little child of luck. Wait, I also have a system specifically for the protagonist? The only requirement is that I become the Great Demon King? This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.