Katainaka no Ossan, Kensei ni Naru

Beryl Gardenant, a middle-aged swordsman running a dojo in the backwaters, lives a quiet life until Allucia, a former student and Commander of the Royal Order of Knights, appears! Beryl’s life is about to change dramatically! City life. Old students. New friends and formidable foes. It’s all too much. But after years of training, he has mad skills, and he’s been dubbed “the backwater swordmaster.” (Source: Amazon Prime Video, edited)