The meaning behind the VOICE in his head, and his eyes.
Okay, two birds in one stone. A quick and dirty not-so-quick and dirty exposition on Shiki's Mystic Eyes as much as I can remember, because proper info is scarce, blast you Nasu, and some background, M.O., and behavioral ticks of Roa. And the difference therein of SHIKI & Roa. More canon details on both can be found here
The Who: Origin
To be concise, Roa was, like all super-badass vampires, once a man of the cloth. In a world where Shinso/True Ancestors were the natural answer to the overpopulation of man, The Church was the one standing power that could oppose their breed. Roa, specifically, co-founded the very branch of the Catholic Church that was allowed to use every trick in the book to see to the sealing and extermination of things that went against the word of God: The Burial Agency. He was a smart man with fantastic talent in the scriptures as well as magecraft based in numerology, and was a fitting opponent against darker forces on Earth. The problem, of course, was that he was also an empty man that desired meaning--something he couldn't find in life. Life ended. Life was bumpy and happy and chaotic but the only constant was that it ended. He didn't like that, and sought a solution, studying the same enemies he constantly fought to seal away. Thus, he came to eventually become infatuated with, fall head-over-heels for, and corrupt one(1)Arcueid Brunestud, the Princess of the True Ancestors. She was tricked into drinking his blood, and in turn, he became a Shito--a Dead Apostle (highest rank classified for humans who turn to vampires by blood-sucking or through magical means).
The What: Shito - The Unnumbered Snake of Reincarnation
There are 27 Ancestors of the Dead Apostles, ranked because of their immense power and age over all other vampires save those True Ancestors that were NOT destroyed by Arcueid (read: those that had choosen to sleep eternally, due to falling to their incurable bloodlust). Most of them adhere to a sick and silly game of territorial conflict, awaiting some promised time when Vampire Jesus (commonly referred to as Crimson Moon Brunstud, the Shinso King) would revive and lead them to some promised land. Which is a falsehood as CM's modus operandi is the extermination of all humans so they'd be out of food hahaha whoops. Anyway, Roa, due to his source/parent of power (Brunestud being a title given to those Shinso powerful enough to be acknowledged as heirs to CM), his own potential power, and maybe a little luck, is accelerated from human to Dead Apostle, skipping the regular progression ladder completely. The upstart upset some of the current chain so much that Altrouge Brunestud, Arcueid's "sister" and Dead Apostle rank number 9, personally went out to end him. Now, some clarification: Arcueid kills True Ancestors that fall and become demon lords and slaves to their bloodlust. Her power is nothing to sneeze at. Altrouge beat her badly enough that her long hair was lost in the conflict.
Roa soundly thwomped Altrouge without so much as breaking a sweat. Task completed, he sought about his work--finding a way to attain eternity. By creating a cycle of reincarnation, he sought to reproduce and live forever, cheating the origin of life, the Akasha, from ever collecting him--intending to survive even past the second coming of Crimson Moon. He because the Unnumbered Dead Apostle, the Snake of Akasha, and a joint effort between the Mage Association, the Burial Agency, and Arcueid herself was made to finally bring him down. But they couldn't seal or destroy him. He'd only reincarnate into a soul of similar thaumatergic origins as his, hand-selected by himself through use of his power and magecraft (yes, predicting THE FUTURE /o/).
This would happen 18 times--Roa would birth in a special individual of high magic potential and high social status, and he'd turn that individual into a vampire, and then destroy the town he was in while waiting for his knowledge and power to fully accumulate. Arcueid would always come along before it got too severe, and usually the city would be saved. Two exceptions were made in this line case: Ciel, and Shiki.
Ciel happened to have a magic potential almost as much as his own, though her social standing was poor. He turned her, and she ravaged her village in record time. Arc came and dealt with the would-be vampire queen, of course, but Ciel's personal ability was so great that death itself did not affect her. But by then, Roa had moved on...to Shiki. Who was of phenominal standing on his own ends (Kishi oni by blood, and in jurisdictional control of a sizable city, where jurisdiction is usually unheard of outside of grants by the Mage Association for workshops).
Shiki's special for a different reason than Ciel, though--his will is stronger.
The Why: Erosion of Ego
As stated, Michael Roa Valdamjong was an empty man, despite his many successes. That's a reason the slaughters that have taken place at his hands are so simple to him. He's regarded as alien, by both humans and Dead Apostles, with completely different motives. The only time he had ever felt alive was the first time he beheld Arcueid at her castle garden. She's his crux and his downfall. But by that point, there's really little left of Roa's original mind and personality.
Despite the awesomeness of his reincarnation, the one flaw is that every cycle erodes his ego a little more. Memories become more mechanical and jagged, and he's left with a template that's simply dominate the host, slay for power, and await the princess. By the time he reincarnates into Shiki, his 18th host, his ego and will are a meager fraction of what they used to be. Far Side of the Moon are tales of Shiki Nanaya's dealings with his own past and that of his adopted family, the Tohno clan. One of the main lynchpins in it that separate it from the Near Side stories is that SHIKI's will to endure and become something resembling human overpower Roa's. While every host Roa's had has been symbiotic, it's also been parasitic, with Roa immediately and completely dominating the mind and soul. Shiki retains pieces of his, to a point where he can resist Roa's M.O. of forming a power network of Dead, base-level vampires.
Shiki kills, but Shiki kills for the love of killing. Roa kills to amass power and to send a signal to Arcueid that he is indeed alive and well, a twisted "I'm home ♥" card if ever there was one. He hopes to witness eternity this way, and doesn't give a damn about who's in his way in the process. This makes him the deadlier of the personalities to deal with, as he has no problems using his cunning and knowledge to destroy all his enemies, and eventually take all of Arc's power away from her.
Not reading it wrong. SHIKI possesses the eyes. In fact, every Shiki in the Nasuverse possesses a set of Mystic Eyes. Only three, however, possess the Chokushi no Magan, Mystic Eyes of Death Perception: Ryougi Shiki, Tohno Shiki, and Nanaya Shiki. And each pair is widely different.
The base of the eyes are that they're a pseudo magic circuit that allow otherworldly sensory information in for the user to affect. It's nature manipulation on it's most base level. And, in this case, the information holds some concept of life or death. In Tohno's case, it's life. He perceives lines and fragmentations on a body, those lines representing the concept of "life", as opposed to N. Shiki's concept of "death". To cut those lines means to seal the life inside the object, similar to cutting the gasline on a car. Without the fuel, the car stalls and dies. UNLIKE the car, the life can't just be restarted or replaced.
Also unlike N. Shiki's eyes, SHIKI cannot perceive dots that represent an absolute life, merely the lines. Nor can he see lines on anything inanimate. So long as the sentient has a body, he can cut the lines, causing a bloodless death of that part or whole of the individual. It matters a whole lot more of where he cuts--a dead/useless arm versus slashing the line along someone's belly and rendering both halves utterly lifeless.
And finally, unlike N. Shiki, SHIKI has no mental penalty or stress to endure. The ability is his to turn on and off as he wills.
The Who: Origin
To be concise, Roa was, like all super-badass vampires, once a man of the cloth. In a world where Shinso/True Ancestors were the natural answer to the overpopulation of man, The Church was the one standing power that could oppose their breed. Roa, specifically, co-founded the very branch of the Catholic Church that was allowed to use every trick in the book to see to the sealing and extermination of things that went against the word of God: The Burial Agency. He was a smart man with fantastic talent in the scriptures as well as magecraft based in numerology, and was a fitting opponent against darker forces on Earth. The problem, of course, was that he was also an empty man that desired meaning--something he couldn't find in life. Life ended. Life was bumpy and happy and chaotic but the only constant was that it ended. He didn't like that, and sought a solution, studying the same enemies he constantly fought to seal away. Thus, he came to eventually become infatuated with, fall head-over-heels for, and corrupt one(1)Arcueid Brunestud, the Princess of the True Ancestors. She was tricked into drinking his blood, and in turn, he became a Shito--a Dead Apostle (highest rank classified for humans who turn to vampires by blood-sucking or through magical means).
The What: Shito - The Unnumbered Snake of Reincarnation
There are 27 Ancestors of the Dead Apostles, ranked because of their immense power and age over all other vampires save those True Ancestors that were NOT destroyed by Arcueid (read: those that had choosen to sleep eternally, due to falling to their incurable bloodlust). Most of them adhere to a sick and silly game of territorial conflict, awaiting some promised time when Vampire Jesus (commonly referred to as Crimson Moon Brunstud, the Shinso King) would revive and lead them to some promised land. Which is a falsehood as CM's modus operandi is the extermination of all humans so they'd be out of food hahaha whoops. Anyway, Roa, due to his source/parent of power (Brunestud being a title given to those Shinso powerful enough to be acknowledged as heirs to CM), his own potential power, and maybe a little luck, is accelerated from human to Dead Apostle, skipping the regular progression ladder completely. The upstart upset some of the current chain so much that Altrouge Brunestud, Arcueid's "sister" and Dead Apostle rank number 9, personally went out to end him. Now, some clarification: Arcueid kills True Ancestors that fall and become demon lords and slaves to their bloodlust. Her power is nothing to sneeze at. Altrouge beat her badly enough that her long hair was lost in the conflict.
Roa soundly thwomped Altrouge without so much as breaking a sweat. Task completed, he sought about his work--finding a way to attain eternity. By creating a cycle of reincarnation, he sought to reproduce and live forever, cheating the origin of life, the Akasha, from ever collecting him--intending to survive even past the second coming of Crimson Moon. He because the Unnumbered Dead Apostle, the Snake of Akasha, and a joint effort between the Mage Association, the Burial Agency, and Arcueid herself was made to finally bring him down. But they couldn't seal or destroy him. He'd only reincarnate into a soul of similar thaumatergic origins as his, hand-selected by himself through use of his power and magecraft (yes, predicting THE FUTURE /o/).
This would happen 18 times--Roa would birth in a special individual of high magic potential and high social status, and he'd turn that individual into a vampire, and then destroy the town he was in while waiting for his knowledge and power to fully accumulate. Arcueid would always come along before it got too severe, and usually the city would be saved. Two exceptions were made in this line case: Ciel, and Shiki.
Ciel happened to have a magic potential almost as much as his own, though her social standing was poor. He turned her, and she ravaged her village in record time. Arc came and dealt with the would-be vampire queen, of course, but Ciel's personal ability was so great that death itself did not affect her. But by then, Roa had moved on...to Shiki. Who was of phenominal standing on his own ends (Kishi oni by blood, and in jurisdictional control of a sizable city, where jurisdiction is usually unheard of outside of grants by the Mage Association for workshops).
Shiki's special for a different reason than Ciel, though--his will is stronger.
The Why: Erosion of Ego
As stated, Michael Roa Valdamjong was an empty man, despite his many successes. That's a reason the slaughters that have taken place at his hands are so simple to him. He's regarded as alien, by both humans and Dead Apostles, with completely different motives. The only time he had ever felt alive was the first time he beheld Arcueid at her castle garden. She's his crux and his downfall. But by that point, there's really little left of Roa's original mind and personality.
Despite the awesomeness of his reincarnation, the one flaw is that every cycle erodes his ego a little more. Memories become more mechanical and jagged, and he's left with a template that's simply dominate the host, slay for power, and await the princess. By the time he reincarnates into Shiki, his 18th host, his ego and will are a meager fraction of what they used to be. Far Side of the Moon are tales of Shiki Nanaya's dealings with his own past and that of his adopted family, the Tohno clan. One of the main lynchpins in it that separate it from the Near Side stories is that SHIKI's will to endure and become something resembling human overpower Roa's. While every host Roa's had has been symbiotic, it's also been parasitic, with Roa immediately and completely dominating the mind and soul. Shiki retains pieces of his, to a point where he can resist Roa's M.O. of forming a power network of Dead, base-level vampires.
Shiki kills, but Shiki kills for the love of killing. Roa kills to amass power and to send a signal to Arcueid that he is indeed alive and well, a twisted "I'm home ♥" card if ever there was one. He hopes to witness eternity this way, and doesn't give a damn about who's in his way in the process. This makes him the deadlier of the personalities to deal with, as he has no problems using his cunning and knowledge to destroy all his enemies, and eventually take all of Arc's power away from her.
Not reading it wrong. SHIKI possesses the eyes. In fact, every Shiki in the Nasuverse possesses a set of Mystic Eyes. Only three, however, possess the Chokushi no Magan, Mystic Eyes of Death Perception: Ryougi Shiki, Tohno Shiki, and Nanaya Shiki. And each pair is widely different.
The base of the eyes are that they're a pseudo magic circuit that allow otherworldly sensory information in for the user to affect. It's nature manipulation on it's most base level. And, in this case, the information holds some concept of life or death. In Tohno's case, it's life. He perceives lines and fragmentations on a body, those lines representing the concept of "life", as opposed to N. Shiki's concept of "death". To cut those lines means to seal the life inside the object, similar to cutting the gasline on a car. Without the fuel, the car stalls and dies. UNLIKE the car, the life can't just be restarted or replaced.
Also unlike N. Shiki's eyes, SHIKI cannot perceive dots that represent an absolute life, merely the lines. Nor can he see lines on anything inanimate. So long as the sentient has a body, he can cut the lines, causing a bloodless death of that part or whole of the individual. It matters a whole lot more of where he cuts--a dead/useless arm versus slashing the line along someone's belly and rendering both halves utterly lifeless.
And finally, unlike N. Shiki, SHIKI has no mental penalty or stress to endure. The ability is his to turn on and off as he wills.