Trackless step explanation

Let's see, humans are nothing more than animals, and like a machine they can't process all the tiny details that they see and hear, and the brain certainly can't consciously recognize all of those sights and sounds. After all, if they processed and analyzed everything they see and hear, the brain will burn out. Therefore, the human brain will toss low-priority information into the unconscious, and abdicate recognizing them in order to ease the load on itself. This thing called Trackless Step is a martial arts technique that applies peculiar breath control and footwork to slip its user's existence into the opponent's unconsciousness. As a result, even though Shizuku can still see Toudou-san, she has become unable to recognize that fact. Even though the brain and the eye can capture Toudou-san's movements, they can't be processed because the consciousness is classifying them as unnecessary information, to the degree that a life-threatening danger can approach to little more than a blink away.