Yagyū Shinkage-ryū
He is popularly credited as the inventor of the fukuro-shinai, a practice sword made from split-bamboo in a leather sleeve, allowing practitioners to practice together and swing with full-force without fear of death or major injury. The particular version used in Yagyū Shinkage-ryū is called a "hikihada-shinai", "toad-skin shinai". The leather sleeve is made of cow or horse hide, but after being lacquered Kamakura Red, it resembles the skin of a hikigaeru.