All Ritual Purification Tracks + where they play.

Yoshiro's vocals could be 'keihitsu', signalling movement of the Goddess.(she's coming/descending) 

It's also vocalized during purification rites and when moving sacred objects. 

But it has many uses... 

Keihitsu meaning "to warn and clear the way." 

Articles: English | Japanese

A video on it: The priest's roar

Youtube AI summary:

Keihitsu (警蹕) is a solemn vocalization or ritual cry used in Shinto ceremonies to herald the movement of a deity (Kami), mark sacred transitions, or invoke a sense of awe and reverence.

Key Characteristics and Uses

• The Sound: It is typically a long, drawn-out vocal sound like "oooooo".

• Heralding Deities: Priests use it to announce when a deity is being summoned to or sent away from a temporary shrine or altar (himorogi).

• Ritual Moments: It is voiced during major ceremonies such as opening or closing inner shrine doors, purification rites (Oharahi), imperial processions, or when moving sacred objects (goshintai).

• Significance: It creates an atmospheric interval of solemnity, serving as a sign for participants to bow their heads and maintain sacred order.

Her vocals disappear(and become muffled) after she begins to petrify, with said petrification beginning at Kamukura Shrine where the Goddess is said to have once descended. 

 Do they disappear because there's no need to signal the Goddess is coming because she's here now?

Kunitsu-Gami Game Design Commentary 28 & 29: Nanamagari(七曲ななまがり)

■第28回 穢れは溜まって縺れる。七曲り

昔に読んだ本に書かれた一文。これがとても印象に残っていてラスボスとして決意。特定のモチーフは無く、人や動物を軸に山に存在する全ての物を内包する様なイメージでデザイン。第一形態は、左右の人っぽい腕が一つの顔を共有して、本体を守っています。

顔は３つの顔が正面左右とくっついて、様々な視点を持つ意味合い。

かなり時期的にも佳境であった為、時間の捻出も大変、ラスボスいつ上げるんですか？と自身の脳内でだけで響かせてました。

動きも色々なアイデアを出して貰って形になり、全体的に見たことない感じに出来たと思ってます。

■Episode 28 Filth Accumulates and Entwines. Seven Twists

A single line from a book I read long ago. It stuck with me deeply, and I decided on it for the final boss. Without any specific motif, I designed it with an image that encompasses all things existing in the mountains, centered on humans and animals. The first form has arms that resemble human limbs on both sides sharing a single face, protecting the main body.

The face consists of three faces attached to the front and both sides, symbolizing various perspectives.

It was quite a critical point in the timeline, so carving out time was tough; I kept echoing in my own head, "When am I going to finish the final boss?"

I got various ideas for the movements and shaped them, and overall, I think we managed to create something with an unprecedented feel.

■第29回　  「真の縺れは確固たる結び　七曲り

こういうのは何か超越した感じですよね…気づいたら出来てました。一心不乱とはこのことかと。

一番重要なもつれを解こうとすると、硬くなって解けない感じをお腹のデザインに入れ、読み取りづらい表情で、身体は人と獣を混ぜ、なんとも得体の知れない禍々しさと神々しさを目指しました。

■Episode 29  "The True Entanglement is a Firm Bond: Seven Twists  

This kind of thing has a transcendent feel to it, doesn't it... It was done before I knew it. This must be what they mean by single-minded devotion.  

To depict the most important tangle, I incorporated a sense of it hardening and becoming impossible to unravel into the abdominal design, with an expression that's hard to read, a body blending human and beast, aiming for an indescribable wickedness and divinity.

Plaque Lore:

山祇やまがみとの約束。山での人の暮らしは豊かさと共に、 植物、自然、眷属けんぞくなど山で暮らすものを脅おびやかすこととなる。その際に生まれる穢けがれ、その全ての穢けがれが山の頂上でもつれ、混沌こんとんとした状態である。 七曲ななまがりの真の容貌ようぼう。全ての混沌こんとんの更さらに奥おくに存在するもの。その姿を見た人曰く、「神か、もののけか…」と。約束を守ることができなかった人々への国津罪くにつつみなのか…。人々の築き上げた物すべてを無に返す存在。

The Pact of the Mountain Goddess

The lives of the people on the mountain are rich, but their very existence threatens the plants, nature, and all other life who dwell there. The defilement is born of their lifestyle, spreading to the peak of the mountain and throwing all life into chaos.

Nanamagari's True Appearance

The being exists in the furthest depths of the chaos. Is it a God? A vengeful spirit? Or is it the divine judge who places humanity on trial for their broken promises? It will return all that people have built to nothing.

No mention of its first form wearing a mask reminiscent of the Goddess.

8 arms and 8 floating spirits(the black little balls) around it.

Nanamagari's true form, the silhouette of the figure appears feminine? Not entirely sure since it's distorted. Though it held the corrupted Goddess in its belly so it's definitely meant to be related to the Maiden.

'Mountain Hag' vibes, perhaps?

I put the Japanese lore into good translate:

A pact made with Yamagami—the deity of the mountain. Human life upon the mountain, while bringing prosperity, simultaneously poses a threat to the plants, the natural world, and the various beings—the deity’s kin—that dwell there. The *kegare* (spiritual defilement) born from this existence gathers and becomes entangled at the mountain’s summit, manifesting as a state of pure chaos. This is the true form of "Nanamagari"—a presence that lies even deeper than the chaos itself. Those who have beheld it ask: "Is it a god, or a *mononoke*—a supernatural spirit?" Perhaps it is a *kunitsutsumi*—a divine retribution—visited upon those who failed to uphold their pact. It is an entity that reduces everything humanity has built back into nothingness.

The English translation should've kept the wording consistent. 

The living creatures of the mountain are called the deity's kin in the Japanese. The word 'kenzoku' is used. If I translate the Japanese paragraph by paragraph, without the others for context, I get one similar to the english: 
Human life in the mountains, while bringing prosperity, also poses a threat to the plants, nature, and other living beings that inhabit those mountains.

The word mononoke... the wikipedia article on it is worth a read. Though I'd like to find a book on it.

I was working on a Nanamgari post but stopped once I saw the design commentary happen. There's not much extra information though.