Katainaka no Ossan, Kensei ni Naru ~Tada no Inaka no Kenjutsu Shihan datta no ni, Taiseishita Deshi-tachi ga Ore wo Hottekurenai Ken~

Beryl Gardernant is a humble sword master who runs a dojo in the Reveris Kingdom.
He had come to terms with the limits of his strength and was living a leisurely life in the countryside.
However, his life changes drastically when Alexia, one of his former students, suddenly visits him and tells him that she has recommended Beryl to be a special instructor within the nation’s Knight Order.
He is reunited with his former students who have become big-shots such as knight captains, top-ranking adventurers, and ace magicians, and he is kicked out of his family’s dojo.
Turbulent times were ahead of him.
Beryl was happy that his former disciples adore him, but he is also humble about the fact that he is not very strong.
However, while he wasn’t aware of it, he was the owner of an unparalleled talent.
Unconscious of his power, Beryl is surrounded by ex-disciples who know of his strength, and gradually makes himself known to the world, all the while remaining rather unaware of all of this.
Source: NovelUpdates