It was made by Izanami so that she could have friends who would not leave her. She taught them to understand speech, which is why the Crafter – the person wielding the Word – is able to command phantoms it creates to do their bidding. Izanami has produced at least four brushes, all of which she has kept with her inside the Underworld until two were stolen from her.
"You wanna dig out my tush-crystal, Yukine?!"
The contents of this article contain manga spoilers.
The phantoms created by the Word are identified using the mask, either in the form of a physical, three-dimensional mask or a simplified two-dimensional symbol.
Masked phantoms are shown to be capable of not just understanding but also producing human speech. For example, the phantom that Tsuyu discovered in Tenjin's residence was able to speak a sentence in answer to her question regarding the name of its master.
Over the course of many centuries, from time to time there have been observances of these masked phantoms appearing on the Near Shore. The Heavens believed them to be "phantoms that are controlled using spells," and assumed that there would have to be a parent or "Crafter" controlling them. The real identity of the Crafter was later revealed to be Father.
The Word can also be used to name shinki. In addition to their regular ability to become a vessel, these shinki are able to transform into a phantom-like state without stinging their master. As such, naming a shinki using the Word has been shown to reverse the deleterious effects of sin-caused blight. In concordance with this, Ebisu's attempts to name phantoms without the use of the Word resulted in his repeated corruption and frequent reincarnations.
Shinki named with the Word
螭Mizuchi / 螭 器Chiki - A monk's staff capable of cracking a shinki's name, exposing the God's Greatest Secret. As a phantom: an aquatic, serpentine creature with the face of a fetus. 莠Hagusa / 莠 器Yūki - A staff with a twisted blade end, which is capable of influencing or entrapping others through its Righteous Net. As a phantom: a wolf-like, humanoid form.