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 ~

Native title: ゲーム開始前に死ぬモブ悪役皇子に転生した俺～推しヒロインの妹と幸せになるために最弱魔法【闇刃】を過剰な努力で極め抜いたら、最強のぶっ壊れ性能と化していた件〜