Mystic Eyes of Death Perception

The Mystic Eyes of Death Perception (直死の魔眼) are a type of Mystic Eyes that are considered to be such a rarity that they are thought not to exist at all. They are possessed by Shiki Tohno and Shiki Ryougi, and Michael Roa Valdamjong in the body of SHIKI Tohno displays a similar ability.

Workings
The Mystic Eyes of Death Perception can be called a circuit the opens up in the brain and eyes to allow the user to "perceive death" in the form of lines and dots. Their usage is not entirely dependent on the eyes of the user, as they can still "see" lines should they go blind. The lines and dots themselves do not actually exist, as they are only perceiving the natural flaws by looking through "deeper channels" than normal people. In perceiving death, it can be said they see the Root itself. The ability to perceive the death of a being or object depends entirely upon the user's perception of death. The brain and the Mystic Eyes work as a set, so having different "specs" allows for great differences in the users' abilities to perceive death.

The eyes do not actually kill "the body", as the power of killing someone's life is very common in the world. The "points" seen by the eyes end the very meaning, the "existence", of whatever is "killed." The destruction, the extinguishing of life that comes afterward, is only a side effect of destroying their existence. This makes it possible to kill the soul without harming the body, allowing for the destruction of one of two souls in a single body without the death of the other soul or the body itself. The weaker soul is the one that will be ended, so it is a battle of strength in that case.

These lines can then be traced with a sharp object such as a knife or a sword which cuts the line (this can also be done with blunter objects such as fingers but this is generally less effective than a blade). Cutting the line “breaks” the object along that line and damage inflicted this way can not be healed or repaired in any way. Healing is possible if cutting the line doesn't completely separate a part of the object from the object itself. Also of note is how Arcueid was cut into a multitude of individual pieces as a result of having her lines traced but was able to survive anyway despite not being able to regenerate. She was able to accomplish this by completely reinventing the conceptual structure of her body, abandoning the conceptual structure that had been traced.

Dots can be pierced by sharp objects. Piercing a dot effectively “erases” that object from existence, in a sense that the object loses even its inherent properties such as momentum, toxicity, and generally any effect it may impose on it's surrounding. Living things whose dot was pierced get “stopped” and, as a consequence, die. While this death may not be instant, it is absolutely permanent, and can't be reversed or bypassed, even by reincarnation.

While Tohno's eyes are normally gray, they glow with blue while utilizing the Mystic Eyes of Death Perception. It is also the dominant color of Ryougi's irises when her eyes are activated.

There are existences that are hard or impossible to kill due to their nature. True Ancestors under the full moon are said to be truly immortal, so there is nothing that can cause their death. While lines and points can be seen during the daytime, they are too close to being "perfect life" during the night that they don't even carry the concept of death. Through enough strain, Tohno is able to see a single line while Arcueid Brunestud is weakened, and cutting her off from nature allows for him to see even more. Against Archetype: Earth, Ryougi cannot see her death, and she goes as far to say that she doesn't have a death at all. Type Mercury and other Aristoteles lack the concept of death entirely, so the ability will not affect them under any circumstance.

Acquisition
Mystic Eyes of Death Perception are a hybrid power, taking aspects of both Mystic Eyes and Pure Eyes. They are acquired through a near-death experience, but their frequency is so rare that they are thought of as nothing more than a myth even by beings like True Ancestors. Simply encountering them makes Arcueid Brunestud call Shiki Tohno a monster due to their unique attributes not found even among the most powerful creatures on the planet. Tohno acquired the eyes after being essentially killed by SHIKI Tohno and immediately sustained by Akiha Tohno's life force. Ryougi acquired the eyes after a two year coma due to being hit by a car and the "death" of her male personality.

Tohno feels great strain from his Mystic Eyes, so he utilizes Mystic Eye Killer (魔眼殺し) glasses made by Touko Aozaki and reinforced by Aoko Aozaki to keep them from being active. Ryougi doesn't show any noticeable strain, allowing her to actively utilize them as much as she wishes.

Differences
The eyes of Shiki, Ryougi, and SHIKI have difference usages and limitations.

Shiki Tohno
Shiki Tohno specializes in kill living things. Unlike Ryougi, he is not suited in the aspect of recognizing "concepts" because he was "submerged in death" rather than touching the Root. He can perceive the death of concrete physical existences, allowing him to kill people, animals, locks, walls, and even part of the planet itself in the form of killing "nature" in a specific area. He views the weakness in a person or object, and ends whatever makes the person or object by striking its point of death. Whatever make a "living person a living person" or whatever make a "hallway a hallway" is ended in the simplest way, unraveling its existence and making it no more. Those who have accumulated an exceptionally large weight of existence take longer to die because there is more of their existence that needs to unravel. While he cannot normally kill concepts, he can see certain things like Akiha Tohno's Caging Hair due to the Mystic Eyes dual nature as Pure Eyes.

He has a great deal of mental strain when utilizing his ability. Due to performing the normally impossible process of his brain classifying the death of non-living objects, it overloads his brain. He will be fine as long as he only perceives what he brain allows him to perceive. Overuse of trying to perceive the death of what he brain will not allow him to normally perceive will eventually overstrain it, causing the blood vessels in his brain to burst and end his life. Overuse without going over his limit can lead to extreme headaches and even temporary loss of sight. He has a hard to perceiving the death of Nrvnqsr Chaos, as he can only see the individual points of death for his beasts. He realizes he would have to kill each individual point in order to end him, but eventually manages to see an "Ultimate Point" below all the others deep in the center of Nrvnqsr's being.

Shiki Ryougi
Shiki Ryougi: Her MEoDP allows her to perceive the death of more or less anything that exists. Whether it is a person, an object, a ghost, a disease, a thought lingering in someone's mind, magecraft, a ward, a psychic attack, etc., so long as it exists, she can kill it. In fact, she claims that if God exists, she could kill him, though Nasu states she couldn't because it isn't alive or dead. So, she basically kills whatever she pleases, although she had some difficulty with killing Souren due in part of the fact that his life force was assimilated with the Apartment Complex where he held his experiments. Nevertheless, Souren himself infers that ultimately she could perceive the death of anything, without exception, if she searched deeply enough. Contrary to what the OVAs may lead one to conclude, her eyes are permanently active, but she doesn't suffer any strain from this.

Ryougi would be able to see lines on a telephone that she perceives as "being alive because it's not broken", but unable to see lines on a broken telephone because it is "already dead" to her. Tohno's brain must open its circuits from the classification of living things to the classification of non-living things to see the death of non-living objects.

SHIKI Tohno
SHIKI Tohno (Roa): Technically speaking, these are not "true" Mystic Eyes of Death Perception; his ability is to see the life force, and it is because he sees the life force, and not actually the death, that these Mystic Eyes of Death Perception are not considered true MEoDP. Consequently, these eyes are limited to killing living things and can be used to directly damage or annihilate someone's life force. Because the flow of one's life is the same as the flow of one's death, the lines overlap, but their origins are different, and therefore the dots don't. His mystic eyes can't actually "kill" like real MEoDP users. Instead, it would just inflict critical damage on someone's life force. So, rather than dying because their "death" has been directly activated, SHIKI (Roa)'s victims die simply because they can no longer live, which leads to their death.