They were made by Izanami for the purpose of having 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 ayakashi it creates to do their bidding. Izanami has produced at least four brushes, all of which she has kept with her inside Yomi until two were stolen from her.
The ayakashi created by the Words are identified using the mask, either in the form of a physical, three-dimensional mask or a simplified two-dimensional symbol. All versions are adorned with an eye. The oldest recorded mask appeared on the island of Tamatsuki. The physical appearance of the masks changed throughout the years, becoming more and more simplified.
If created using earlier versions of the Word, masked ayakashi may have various weaknesses, including the following:
- Being unable to survive in direct sunlight.
- Dying after a single "use" (presumably, after fulfilling a command).
- Requiring a physical mask made by the Crafter to be born.
Masked ayakashi are shown to be capable of not just understanding but also producing human speech. For example, the ayakashi 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 ayakashi appearing on the Near Shore. The Heavens believed them to be "ayakashi 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.
"You wanna dig out my tush-crystal, Yukine?!"
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我が 僕とす/ ひとつ 名のもと 伏せ / 従え 人 形となし 留め 置かん / 器は「 莠」 / 名は「 莠」
(Original Japanese text)
Wa ga shimobe tosu / Hitotsu na no moto fuse / Shitagae hitokata to nashi tome okan / Ki wa [Yuu] / Na wa [Hagusa]
I dub thee my servant. Bow down to the one name. I call thee to human form and bind thee to it. The vessel, [Yuu]. The name, [Hagusa].
(Official English translation)
In addition to their regular ability to become a vessel, these shinki are able to transform into an ayakashi-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 ayakashi 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 an ayakashi: 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 Goodness Net. As an ayakashi: a wolf-like, humanoid form.
The Crafter can command masked ayakashi to possess a human, thus leaving the human under the Crafter's control. However, it is unspecified whether this ability is specific to the second Word in Father's possession, or if he was simply unaware of this ability while he was wielding the earlier version of the Word.