The biggest difference between the Youbi Sword Drawing Skill and the Yagyu Sword Drawing Skill was that the Youbi Sword Drawing Skill could be nurtured with reiki.
The Yagyu Sword Drawing Skill mainly depended on sword power and mind energy. However, a person's daily mind energy was limited. This was what he found out when he observed Yagyu Kenichiro last time. hHe realized that even though Kenichiro conserved his sword power for a few years, the release of his moves were not able to defeat him.
