The World's Least Interesting Master Swordsman: Volume 9 by Rokurou Akashi

With the strongest swordsman around, the kingdom of Sepaeda has nothing to fear. If his master wills retribution, then he will deliver it.
Douve and Tahlan, Happine and Saiga, Setenve and Ukyou... All three couples are set to have a beautiful wedding ceremony together. And thanks to the otherworldly arrivals, Arcana has been developing by leaps and bounds. This rapid growth, however, has its neighboring nations on edge. They’re afraid, awestruck, anxious, and above all, envious. Blinded by jealousy, they insult Tahlan personally. Sepaeda’s young leader immediately leaps to his defense—and he has no plans to keep things civil!