When My Younger Sister Enrolled in a Female Knight Academy, She Somehow Became a National Hero. Or R

This young man had sent his younger sister to a Female Knight Academy and was supposed to be thinking about what to have for dinner tonight, whether it should be soba noodles or grilled fish. However, he somehow ended up eating with the daughter of a duke who was also the student council president. Before he knew it, he had met a princess and was worshipped by an Amazon who was supposed to hate men, and then—

Despite being an ordinary commoner (at least he considers himself to be), he somehow became a national hero as a result of protecting the backs of busty beautiful girls and saving their lives in a battle he got involved in. This is a relaxed and heartwarming, almost cliché-like story of a young man who somehow became a hero of the nation and rose to success.