Mystic Eyes of Death Perception

The eyes possessed by Tohno Shiki, that can see the death of things.
This death is expressed as black lines and points. However, the lines are nothing more than places where a substance breaks easily, while points are death itself.
If a line is cut, then even if the main body survives, that particular part will die, never to move again.
If a point is pierced, then the individual will stop functioning completely.
Though they are said to see the form of death, strictly speaking it’s more accurate to say they’re reading the lifespan of a substance—the existential limit determined at the moment of creation.
Now, this was already covered in the main story of Tsukihime, but lines cannot be perceived on things that can’t be killed (destroyed) in the current world. It’s probably because as a human, Shiki’s point of reference conforms to the limits of the humanity of his era.
If he tries to perceive the death of things that exceed those limits, Shiki himself will begin to break down.
Originally, Shiki’s eyes were meant to “see that which cannot be seen.” However, after having two near death experiences he was somehow connected to (the Root), and his brain began to be able to comprehend death itself. Or to put it in other words, it is only by virtue of his mystic eyes and brain working together as a set that he is able to perceive death.
By the way, Shiki’s eyes turn blue when he intentionally tries to see death. Seeing as how blue is the color of pure eyes, it’s likely that Shiki’s eyes are also of that type.

Tsukihime Data Collection: Tsukihime Dictionary
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The eyes possessed by Tohno Shiki, that can see the death of things.
This death is expressed as black lines and points. The lines are places where a substance breaks easily, and the points are death itself. If a line is cut, then even if the main body survives, that particular part will die, never to move again. If a point is pierced, then the individual will stop functioning completely. Also, while lines can be seen without consciously trying, seeing points, the source of those lines, requires extreme concentration.
Though they are said to see the form of death, strictly speaking it’s more accurate to say they’re reading the lifespan of a substance—the existential limit determined at the moment of creation. Now, this was already covered in the main story of Tsukihime, but lines cannot be perceived on things that can’t be killed (destroyed) in the current world. It’s probably because as a human, Shiki’s point of reference conforms to the limits of the humanity of his era.
Originally, Shiki’s eyes were meant to “see that which cannot be seen.” However, after having two near death experiences he was somehow connected to (the Root), and his brain began to be able to comprehend death itself. Or to put it in other words, it is only by virtue of his mystic eyes and brain working together as a set that he is able to perceive death.
By the way, Shiki’s eyes turn blue when he intentionally tries to see death. Seeing as how blue is the color of pure eyes, it’s likely that Shiki’s eyes were originally of that type.

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised
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The eyes possessed by Tohno Shiki, that can see the death of things.
A unique ability that allows the user to grasp the death of living beings as points and lines. Stabbing or cutting these will ignore things like vital activity and kill the target directly.
Though they are said to see the form of death, strictly speaking it’s more accurate to say they’re reading the lifespan of a substance—the existential limit determined at the moment of creation.
Lines cannot be perceived on things that can’t be killed (destroyed) in the current world. It’s probably because as a human, Shiki’s point of reference conforms to the limits of the humanity of his era.
Originally, Shiki’s eyes were meant to “see that which cannot be seen.” However, after having two near death experiences his brain began to be able to comprehend death itself. Or to put it in other words, it is only by virtue of his mystic eyes and brain working together as a set that he is able to perceive death.

MB Act Cadenza PS2 Manual: Tsukihime Dictionary
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The supernatural power that manifested in Tohno Shiki as an after-effect of the incident from seven years ago. Mystic Eyes that can grasp the concept of “time of death” naturally embedded within all of creation ——— “lines where things can die easily.”
One of the “phenomena that cannot be achieved under any circumstance” in opposition to the “physical phenomena that can be achieved by modern technology.” By tracing the “lines of death” it is possible to sever the target and impart death (this is not killing by severing the target, but rather the target being severed as a result of killing it).
With the “Mystic Eye Killers” glasses received from his mentor (Aozaki Aoko) in the past he can suppress his power to a level where does not impede daily life, but when Shiki finds himself in an extreme situation the glasses cannot suppress the power of his eyes from welling up.
Ultimately it is possible to trace the “lines” or “dots” of not only living things but also non-living things, and even perceive the death of any kind of space or existence.

Tsukihime Material I: Tsukihime Work Glossary
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The peculiar ability possessed by Shiki, our protagonist. Categorized as a psychic ability.
He can see the normally imperceivable “lines of death,” something akin to the point of collapse in all things.
These lines of death are like seams, which means all it takes to sever an object is to run a blade through them.
The strength and hardness of the object does not enter the equation. No matter how hard or frail, the feeling is always the same. Perceivable = Cuttable.
In addition, as things dismembered by the lines of death “kills” that specific part, healing is impossible. This is because the severed part has died on the existential level, even if it only looks like it has been cut.

Shiki is a living being and thus he’s able to better understand the death of things that are alive, same as him—this is why he unconsciously perceives the lines of death on the living.
However, Shiki himself can stress his consciousness and overexert his eyeballs to visualize even the ordinarily incomprehensible lines of death on inanimate objects, and through this, he can perceive even the “death of space—or, death of existence,” as an ultimate locality. (Shiki’s brain is unable to withstand seeing the lines to this level)

In addition to the lines of death, there are the points of death, which are a grade above the lines.
If the lines of death can be likened to blood vessels, the points of death are hearts.
Those that have had their point of death pierced are killed in literally a single strike. Just as in the case with the “death of space,” Shiki has to overexert himself if he wants to be able to see them.

It’s important to note that while the lines of death exist in all things, there are differences in how distinct they are.
Putting it simply: the lines of death are lifespan.
He can easily perceive the death of humans who only have the lifespan of about fifty to a hundred years, but it is difficult for him to perceive the death of existences who possess a lifespan in the hundreds or thousands of years.
Meaning, as long as he is trying to perceive the concept of death as a shape, he cannot quite so readily grasp it coming from things that are difficult to kill.
This is why when Shiki is up against Superior Dead Apostles1 or Arcueid in the story, he has to push his consciousness to the limit if he wants to perceive their death.

(*Superior Dead Apostles are hard to kill, while Arcueid cannot die. Shiki’s murder of Arcueid in the beginning of the game made the impossible possible. In the Tsukihime world, that Arcueid would die or be killed is something very much out of the norm)

Translator’s Notes
  1. ^ Superior, greater, or upper-class Dead Apostles.
Katatuki Kouhon: World & Tsukihime Character Setting