Imouto ga Onna Kishi Gakuen ni Nyuugaku Shitara Naze ka Kyuukoku no Eiyuu ni narimashita. Boku ga.

My little sister enrolled in an all-girls academy that trains aspiring knights. Even at this academy, renowned as the most prestigious in the kingdom, my brilliant little sister still easily displays her overwhelming prowess! "Nii-san, I told you already—you're much stronger than someone like me!" No, I'm just an ordinary commoner, you know... (※That's a lie. Nii-san is insanely strong. He just doesn't realize it.) Because of that, a female knight from the academy appeared and challenged me to a mock battle. (※The strongest female knight in the academy instantly realized the difference in their strengths.) Then, I gave her some post-battle care. (※The female knight enjoyed Nii-san's massage so much that it became popular among the nobility.) And just by doing what I normally do, I caught the eye of the QueenーEh? Why!?