The Magical Revolution of the Reincarnated Princess and the Genius Young Lady, Vol. 6 (manga) — Piero Karasu

Prince Algard and Princess Anisphia have always been close as siblings. But as the heir to the throne, Algard has grown disillusioned over the years—with his sister, with magic, and with the kingdom he is destined to rule. Unsatisfied with merely being a cog in the machine, he launches an attack on Anisphia’s detached palace…with the goal of obtaining Lainie’s great power for himself! At last, brother and sister shall face each other in a heated clash over the future of the kingdom!