Shinkage-ryū

Until Kamiizumi, swordsmen practiced their art with either a very hard wooden sword (bokken) or one with a dulled steel blade.

Kamiizumi created a practice sword made of a length of bamboo, split two to 16 times on one end, and covered in a lacquered leather sleeve.

Kamiizumi, sensing the changes in the ways of war at the time, re-thought his methods of martial arts and began to advocate the utilization of light armour during training.

The face of war was being transformed, and as it was necessary to move faster than before, Nobutsuna perfected a style of sword "freer" in its movements, more sparse, more restrained, more adapted to brawls and to duels than the fields of large-scale battles.

Kamiizumi did not have children and left all his property and his school to his student Yagyū Sekishūsai Muneyoshi (柳生 石舟斎 宗厳 1529–1606).