Also, I like the idea of a clan of ninjas that still uses Ninshu, or perhaps a direct derivative, as a set of hiden. Maybe a close relative of the Yamanaka, or perhaps the Yamanaka themselves...Or perhaps both. Their relative literally uses ninshu, while the Yamanaka use derivative mind manipulation arts. Injuries are mirrored because ninshu connects mind to mind and body to body.
He was a superpowered peace seeker who taught them a means by which true peace and understanding could be achieved. Then they used it to give themselves magical war powers instead.