Sympathy

"This is an example of sympathetic resonance." The professor had instructed back then with a mundane tone. "Measure the distance, frequency, and amplitude and note them down in a table in your lab journals."

If anybody had told young John that he would one day be using this principle to create a fighting technique to kill other Martial Artists, he would have looked at them with a strange expression before moving away.

But it came to be. 

Rui's idea was simple. The principle of sympathetic resonance allowed for one to pass on vibrations to a target through sound as long as the frequency of the vibrations matched the innate vibrating frequency of the target. Every object had an innate vibrating frequency, it was possible to vibrate an object and even cause it to generate force as long as said was exposed to sound of the same frequency.

In fact, this was the same principle that was used in MRIs, lasers, and even electrical circuits.