So the technique uses the basis of wavelengths that are in everything and does something similar to mirio where he phases through stuff like a wall, the floor. He can also do the same thing with stuff like sound, air. He syncs with a passing wavelength, in most cases it’s sound, and has to travel through the whole wavelength cuz it’s intangible, not physical like a building or something. But, in order to do damage since his curse technique can’t do direct damage, he experimented and found out that by deactivating his curse technique while he was still phasing made his solid wavelength clash with intangible wavelengths. This clash causes the shatter and the faster and more sudden the deactivation is, the more powerful the shatter becomes. However, he can’t just do speed of light because going at that speed would kill him. Speed of light means you have no mass at all. You’re a photon. So the limits of his technique are that he can’t stay phased in intangible things for too long or he gets fried, and he can’t go to a wavelength faster than sound since it’ll literally break his body apart going at that wavelength.