Sagawa's "famous" comment about breath training being unnecessary and not useful, was very interesting to see and consider within the fuller context of his training and skill level.
The process of learning certain types breath-control is a tool in developing the ability to manipulate force inside the body, for outward expression as power. At first, as with any movement or action when one is just learning it, the breath is "big," audible and obvious; later, it becomes minute and quiet, but the power is there. At that point, it has become "natural" to the body, and a condition that one can hold without overt effort. Sagawa probably just stopped cognitively thinking about it altogether because there was a level of his consciousness that was quietly overseeing it. "Eh. It's no big deal..."
Yeah, this makes me wonder if a comment that I received from a high-level guy that "at first you need breath and intention to activate ki, then later you don't need the breath so much" has come down from Sagawa, or if it is more ambient than that.