やがて黒幕へと至る最適解, The Optimal Solution to Eventually Becoming the Mastermind, What It Takes to Become the Mastermind : The Optimal Path, The Optimal Solution Leading to Becoming the Mastermind, Yagate Kuromaku e to Itaru Saiteki kai

After losing his beloved lifelong master, Artesia, and swearing vengeance against those who betrayed her, Kartz completes all his preparations and returns to the past. Now reborn as his 10-year-old self, Kartz begins to move in the shadows — armed with the knowledge of the future — to fulfill his revenge as the true mastermind.