Musashi is one of the many people who tried to learn Genkai's techniques. Musashi fought Kuwabara in the fourth test and lost. Musashi has the ability to mask his spirit emissions so that he can't be seen in the dark by people with high spirit awareness (such as Kuwabara). He also uses a sword carved from a holy tree washed in a sacred stream. When a piece of it broke off, Kuwabara used it and discovered his Spirit Sword abilities.