From Old Country Bumpkin to Master Swordsman: My Hotshot Disciples Are All Grown Up Now, and They Won't Leave Me Alone Volume 6 oleh Shigeru Sagazaki

Beryl has finally achieved a lifelong goal: He defeated his father in a one-on-one sword fight! And now that he’s beaten the greatest swordsman he knows, Beryl’s confidence finally starts to grow. Just as he begins to channel his newfound energy into teaching, Beryl receives a sudden invitation to a party being held by Margrave Flumvelk. Beryl isn’t at all comfortable among high society, but since his presence was requested by Princess Salacia herself, he has no right to refuse. So, he and Allucia set off to a noble’s mansion! Lavish meals, a dazzling party full of wealthy, influential people, and a warm welcome from a beautiful young lady—Beryl is faced with a level of luxury that makes his head spin. However, when a powerful new opponent appears before him, Beryl must brandish his blade and put his newfound confidence to the test!