In addition, there was a story that Nagayasu appealed to Ieyasu that he was one of the excellent officials accepted even by Shingen and that he had knowledge about gold mines through Masakazu NARUSE (a warrior in the Warring States period), who was a former vassal of Takeda family and the close servant of Ieyasu, and consequently began to serve under Ieyasu.
また、一説では家康の近臣で、旧武田家臣の成瀬正一(戦国武将)を通じて自分が信玄にも認められた優秀な官僚であり、金山に関する才能に恵まれていることを売り込んで、家康に仕えるようになったともいわれている。