The true nature of this inscription is still shrouded in mystery.
When applied to an object, it increases its durability by many times, even if the components of said objects are not fused together. For example, Killua, whose superhuman strength allows him to easily twist any iron box open, was unable to warp Ging's box in the slightest. However, any object bearing the inscription will break immediately if it comes in contact with Nen, as first shown when Gon's promise string tore after he used Ten. According to Killua, this is because the inscription has similar powers to Nen. Wing obscurely claimed that the promise string had broken because he had infused his own Nen in it, hinting at the possibility that the inscription needs one's aura to be effective. It is unknown if it is related to the God's Letters.