Re:Monster Vol. 8 by Kogitsune Kanekiru

THE NOBLE FACTION STRIKES!

With the assassination of the minister's grandson, the Noble Faction launches a coup d'etat! Accepting his new role of suppressing the rebellion with his signature grin, Rou withdraws his employer, the tomboy princess, to a secret location. There, he continues training the palace guard, using Noble Faction troops as target practice! However, the Faction's two strongest warriors—the Hero of Lithic Iron and the Hero of Turbulent Waters—remain unscathed. While the Hero of Turbulent Waters is out of the city on duty, Rou and the princess take the chance to penetrate the castle...