The many forms of "Nothing" in Type-Moon.

You’ve probably seen Type-Moon throw around terms like “Emptiness,” “Hollow,” and “Nothingness” across different works. At first, they may sound interchangeable, but they’re not. In fact, Type-Moon presents two fundamentally different kinds of “Nothing” with entirely separate meanings and implications.
This short thread breaks them down and explains why they shouldn’t be confused:

1. Hollow:

Hollow represents the "nothing" of physics and mathematics: an absence that exists within a defined system rather than true nonexistence. It is closely tied to imaginary number space, a mathematical construct used to represent potential solutions to problems that cannot be resolved within the real-number system. This concept extends into metaphysics: Hollow embodies the possibilities that could exist but have not yet manifested, acting as a container for unformed potential within an already-defined reality. 

This relationship is exemplified in the Moon Cell, which divides its structure into two layers:

• The Near Side, which observes and regulates reality, analyzing the "true" state of existence.
• The Far Side, which functions as a repository for discarded possibilities, akin to a "trash bin" where unrealized or rejected data accumulates.

BB’s domain, the Far Side of the Moon Cell, is an expression of Hollow: it does not shape new realities but instead stores abandoned ones, acting as a space of unrealized potential rather than true nothingness. This ties directly into the implied power of the Crimson Moon: the ability to mold the ideal state of reality by navigating between what is and what could be, aligning possibility with desired outcomes. This mirrors the function of the Moon itself as described in Kara no Kyoukai: a fixed point in a sea of chaotic potential, capable of observing all possible paths and selecting the optimal one:

The coldness of the night sky stands out just much as the coldness below. If the town is the deep sea, then the sky is just pure darkness. In the darkness, stars glitter like jewels. The moon is a void in this darkness - a large hole in a big black canvas known as the night sky. So that thing is really not a mirror of the sun, but rather a view of "the other side"... That's what I heard at the house of the Ryougi. According to them, the moon is a gate to another world. Kara no Kyoukai Chapter 1

Hollow is the element of Angra Mainyu, the embodiment of formlessness. It does not create, nor does it define: it simply represents a lack of shape, a sea of potential that awaits imposition of order. This is why Angra Mainyu has absolutely no genuine connection to the Root. The Holy Grail, tainted by Angra, cannot go beyond the constraints of the existing world; it can only fulfill wishes within the framework of established reality, no matter how extreme they may seem. Contrary to misguided expectations, it is not an omnipotent wish-granter, it is simply a vessel for the twisting of reality rather than its redefinition.

In short:

• Hollow is not true nothingness. It is an absence within a structure, an unrealized possibility rather than an absolute void.
• It lacks inherent form or existence but is constrained by the framework of a defined reality.
• It represents potential, but only within the boundaries of what is already established.

Thus, it is infinitely more limited than the actual "Nothingness" from which all things emerge. Avenger has a distinct conceptual definition: he embodies evil and the potential forms of evil in the world. While he may not have a fixed shape, he still represents something, evil itself, making him different from true nothingness. His concept gives him meaning and definition, even though he might lack a static form.

Avenger's "hollowness" comes from the fact that he is not a fully realized entity but rather a potential form of evil. His existence is tied to the current reality of Earth, meaning he is shaped by the concept of evil as it manifests in this world. His potential is not infinite, and it is bound by the parameters of Earth's reality.

Thus, Avenger is not true nothingness because he embodies a concept: evil and its potential forms. True nothingness, however, has no inherent concept or potential. Avenger, despite his lack of fixed form, is still something, defined by his concept of evil, whereas nothingness lacks any form of definition or potential.

2. Nothingness ( " " ) – The Root, the True Void:

This is true Nothingness, the absolute void from which all existence originates. Unlike Hollow, which is the absence of form within a system, this Nothingness is beyond any framework or limitation. It is the Root: the source of all possibilities, all concepts, and all manifestations of reality.

Void Shiki explains this directly in the epilogue of Kara no Kyoukai:

—The swirl of the Root is a "place" where all causalities interlace, where all things are in potential, and therefore where nothing is whatsoever. - Kara no Kyoukai Epilogue

The Root is called "Nothing" because it lacks a proper definition. Since it contains all possible things, it cannot be described in finite terms; any given name or concept is inherently a limitation, an attempt to confine something boundless within a specific definition. Thus, it is not called "Nothing" because it lacks substance, but because it defies categorization altogether:

If you really wished to pronounce this term, call it “Kara.”Its meaning varied depending on each individual’s understanding. To put it in simple terms, it was the Spiral of Origin. However, since the Spiral of Origin was called the Spiral of Origin, it was no longer “ ”.To properly express this term was a source of headache during the production of the drama CDs. -Garden of sinners Pamphlet: Kara no Kyoukai Settings Glossary

This is true omnipotence, not in the sense of absolute power, but as infinite potentiality. The Root is not an entity, nor a force, nor a being. It is simply the source from which all things emerge, containing within it:

• All forms of space and time
• Every possible concept and its negation
• All potential realities, including those that are never realized

Shiki Ryougi’s Origin is Nothingness itself. Her very existence is an extension of this boundless potentiality. This is the reason for:

• Her killing instinct, which is not merely a desire to destroy but an impulse to return all flawed things to Nothingness, where contradictions no longer exist.
• Her Mystic Eyes of Death Perception, which allow her to perceive the flaws and boundaries of all things, and thus return them to " ", erasing them from existence itself.
• Her instinctive ability to master any skill or technique, because "nothingness" means infinite adaptability: she has no predefined limitations, allowing her to become anything, perform anything, and execute any action flawlessly. Her very name, "Shiki" is a term used to describe a program capable of performing any given task to an exceptional degree:

“The Ryougi family solved that problem by imbuing one body with a countless number of personalities. It’s the same as a computer. If you put hundreds upon hundreds of pieces of software into one piece of hardware called Shiki, a professional in all areas is created. That’s why her name is Shiki. The Shiki kanji in Shikigami. The Shiki kanji when you talk about Mathematical Formulas. A program that fulfills any task required of it perfectly. An empty doll that possesses countless numbers of identities, and can be modified by putting in another personality with different morals, thought patterns, even senses.”

Did Shiki already know of this..? Yeah, she definitely knew. That’s why she had stubbornly avoided becoming friendlier. Accepting the fact that she wasn’t an average person, the fact that she had not been born into a normal family, she had just been trying to live a quiet life.

“This is a continuation on the subject of the Taiji, but the division of the chaotic 「　」 into two is Ryougi. In order to further stabilize this, and in order to increase the number of classes available, they divide it into four phenomena. They then further increase the complexity by cutting it into eight trigrams. Like this, they keep dividing by a base of two. This, too, could symbolize Shiki’s ability. But that no longer exists. A bug appeared in the perfect program, you see. The Shiki you see now, well, there may be slight problems, but she is a perfectly normal human with self-awareness.” - Kara no Kyoukai Chapter 5

If Hollow represents what could be, then the Root is what allows for anything to exist at all. It is the perfect whole, where "everything and nothing" exist as a singular, undefined truth. This is the ultimate contradiction: in its absolute completeness, the Root is also absolute emptiness.

This passage provides even more insight on " " :

He had sufficient awareness to understand how she escaped the imprisoned space. Last night, the young lady had lost consciousness after several of her ribs were shattered by the Magus’s blow.

She had just recently awakened within the closed space, in the boundary set between the walls of the apartment complex. Within that impossible space she slashed through the impossible wall.

Infinity is not 「 」. For infinity to remain infinite, the finite has to be defined. Without the finite there cannot exist infinity. Because things have an end, we can observe the thing called infinity.

Ryougi Shiki had been cast into infinity, she saw the impossible finite and cut through it.

Of course, there is no finite inside of the infinite. You can’t slash through what doesn’t exist, so escape from such a cage is impossible. But, if there is no finite then there is no infinite. Whether finite walls exist or not, an endless world holds no meaning before Ryougi Shiki.

If there really is no finite, then it’s not infinite but 「 」. If the finite can be comprehended, Shiki could detect and slash through it.

... The black hole that should have been absolute was just a small dark room to his opponent. The Magus felt ashamed of himself. - Kara no Kyoukai Chapter 5 Kara no Kyoukai Chapter 5

Even infinity is not true "nothingness," because infinity is defined by its properties and by the distinction between Araya's realm and the external reality it resides in. This distinction allowed Shiki to "kill" the boundary and return the Void to a state of True Nothingness, which lacks any kind of boundary.

For something to be considered infinite in relation to something else, there must be a separation between the two. The infinite requires a finite boundary to define and differentiate it. Without this distinction, infinity loses its meaning, as it can only be conceptualized as something extending beyond a limitation.

In the case of Araya's void (or any concept of infinity), it exists as a distinct entity because it is separated from the external world by a boundary. This boundary marks the limit of known reality, and only through this limit can we discuss infinity in relation to it. Without such a boundary, the concept of infinity wouldn't exist in any practical sense: It would dissolve into an undifferentiated state, akin to nothingness.

Thus, infinity needs a context or limit to be recognized. Without separation from the finite world, it becomes an unobservable, ungraspable concept. This mirrors the passage, where even an "infinite" space, like the closed world, doesn't hold meaning unless there's a clear boundary distinguishing it from the external world.

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So we have seen there are two main types of "nothing" referenced in the verse: Hollow is the "nothing" of shape and form; the unrealized states of existence that could take shape within reality. In contrast, true " " refers to the "nothing" of abstraction; the realm where the very ideas behind all form and structure reside. These abstract ideas, being immutable and perfect, require no change or interaction. From the standpoint of reality, which can only engage with interpretation and form, such pure abstraction is truly "nothing", a silent foundation that cannot be reached, only echoed through the possibilities Hollow offers.