I Reincarnated as a Mob Villain Prince Who Dies Before the Game Starts ~ In Order to Be Happy with My Favorite Heroine’s Younger Sister, I Overcame My Weakest Magic [Dark Blade] with Excessive Effort, and It Became the Strongest Broken Power ~

Huh? When did my fallen-into-darkness little sister start obsessively worshiping me like a yandere? I, Luke, the 5th prince of the Celestia Empire, had a younger sister. She was Diana, the world’s cutest sister who loved me. However, she was fated to fall into darkness and die. This is the world of the RPG game “Crisnights,” which I played in my previous life, and Diana would become the demon king who gets killed by the hero. My beloved sister dying in despair? I can’t allow such a future. I decided to fight against fate from when I was a baby. Diana fell into darkness because our mother was assassinated, and our father, the emperor, used her as a tool of war. I’m going to thoroughly...