Imouto ga Onna Kishi Gakuen ni Nyuugaku Shitara Naze ka Kyuukoku no Eiyuu ni narimashita. Boku ga. - Ch. 1

[ScryedParadox]

The massage was just the preliminary warmup. The real training involves sword training with his sister, constantly stabbing her with his legendary chunchunmaru blade until she collapses from the overwhelming intensity of the training. That is the true alabama way of training to the peak of power that she is at, and his body simply became more resillient and immune to all physical wear, tear and fatigue due to that constant aggressive combat... Well, if there was an erotica tag anyways.