Death, in all fairness is the splitting of any bonds a soul has from its body, like ripping muscles from the bone. On a spiritual level, as the souls bonds break one by one, the parts of the soul that aren't bound to the body try to rip themselves away from the body. This force means the other bonds still intact are under increasing pressure, like tug of war, and the more bonds broken means the quicker other bonds will break because they cannot withstand that force.
A soul is a concept unexplainable, spiritual energy is one half of chakra energy, it is the fortitude of the mind and soul. The more spiritual energy a soul has does not mean a stronger body or a stronger mind however, it is a result of a mind becoming stronger in a lifetime that makes the soul grow. Spiritual energy fortifies the bonds between body and soul, but as the spiritual energy grows a person must also cultivate physical energy and their body alongside it.
The imbalance of spiritual energy to physical energy is one that is much more dangerous than if it was an imbalance of physical energy. If the spiritual energy of a soul becomes too much for the vessel to bear, then in return the soul's bonds grow too large for the vessel. The soul falls away from the body, even if the body is still functioning and 'aware', a soul is what gives the body the ability of free will and to transcend instinctual behaviour.
When a soul is too strong for a body, it rejects it, and in turn the body becomes catatonic in nature. There but the 'person' is gone. Falling into the void as the soul is torn from its host.
Itachi was a man of impressive mental fortitude, but also a man of deteriorating physical capabilities. As his body grew weaker due to his mysterious illness, his soul grew to bursting in the weakened body. His soul bonds had already started to snap as his body grew closer to its death by the lungs irreparable damage. Which made his death faster. But his soul had melded so intimately with his living self that it even death would not wipe clean the influences of Itachi's life.
The Pure World was a place where souls would experience a peace that would slowly mold their souls back into undamaged, unmarred and 'blank' souls. Where their memories and their lifetime would be taken from them and they would revert back into new souls, however they would keep what affected the soul in a lifetime. Their spiritual energy although purified would still hold vague concepts of their past lives.
Itachi's soul was too shapen, too iron willed to be melted and undone of the lifetime it had –as- Itachi Uchiha. But it had no body.
But when hunger for life was concerned, beings that trod the line between life and death quite often noticed souls like Itachi's. Ones that would give them the ability to tread into life, to take in a soul as a host. They would fill their empty bodies with the soul- that would in turn take shape and become what it was so desperately hanging onto. But souls like the ones beings believed they could use to experience life, they were too strong and would overwhelm the wisps that gave the almost empty things minds. Bury them under the weight of a lifetime.
And as that ghoulish being took Itachi's soul into it's blank vessel, it's large wisp of being was pressurized and buried under the force of man that was Itachi Uchiha. It's amalgamous form contorted and rippled as it's being became Itachi Uchiha.
However, that as it was, the ghoulish being's body was so much stronger than Itachi's previous, and Itachi's soul almost immediately made bonds with the body so tight it could be likened to titanic forces or immovable and unstoppable power. Itachi Uchiha, in this body- this new, different... "larger" being- would not die easily.
For even if Itachi was still Itachi in Soul and in appearance. The being that had taken in his soul was so far from human yet almost so close... Itachi was not the same, and would not be the same as he would soon realise. For even shinobi did not desecrate a body in the ways that the Ghoulish Entities existences required.
And in the few moments before that wisp of a mind was crushed, It laughed.
Because even if Itachi had taken It's body? It would be there, It would lurk, circling the edges of Itachi's soul like a starved hyena, content with watching because Itachi would not be able to escape It's needs.
Even if It had failed in being able to experience life as It's own being? Oh, It would howl, and shriek with mirth because Itachi was a Ghoul. And It knew, that Itachi would find his own body disturbing. It was content, with what had happened, because this was better entertainment than what It had in mind.
It would let Itachi use It's unholy being and inhumane power how Itachi wished, even if at the base of It's core It knew It could not actually stop Itachi. Because as glimmering, mirrorlike shards in a maw of shadowy darkness pulled into a wicked grin, with hollow sockets of gore and viscera glinting in the darkness beneath Itachi's feet...
It knew It would have so much fun watching.
Sensation was not a thing Itachi was familiar with experiencing during death.
Sensation was described by "a physical feeling or perception resulting from something that happens to or comes into contact with the body.", and Itachi was certain that he had lacked a body.
But there's a distinct lack of a lack of sensation and he can hear someone laughing as if they were cackling loudly from the other side of a battlefield with water in his ears- and he doesn't know what's going on.
And he feels himself twitch involuntarily, and suddenly his mind focuses on all the limbs he suddenly has which he did not have before, eyes that he hadn't had earlier.
The darkness around him that swallows his senses.
Sensation was not an experience those who are dead experience, sensation was the cause of a body's nervous system. Itachi knew an extensive amount on how sensation was simply the reaction of electrical signals and touch receptors, all hinging on the existence of a body being present. Death was the release of everything, and because sensation was the result of having a body-
It meant that logic would dictate that the limbs and appendages he feels he has aren't his imagination, Death dulls the mind to everything around it- so the imagination could not procure something that felt so real. And following that logic, Itachi could only come to one most likely conclusion.
He was alive, which he wasn't supposed to be. Itachi had a body, which he was not supposed to have either. Both of these facts seemed almost surreal, and his subthoughts muttered through a haze to his surface mind that it would probably be a time before Itachi realised the connotations and- perhaps, consequences, of such a thing.
And as Itachi went to take a step forward, where there was supposed to be solid ground beneath his next step- it's gone. With his stomach dropping in a feeling akin to missing a step on a set of stairs, Itachi falls into crushing nothingness, falling faster and faster.
Running through various calming techniques in his head in what feels like a split second, Itachi spun as his instincts blared at him for a moment, summoning a thin layer of chakra to his feet as he felt himself land.
Breezily transitioning into a crouch in order to save the strain of his landing, Itachi's eyes slowly slid open. And they started to sting, eyes watering as at the same time an awful smell rose to greet him. His stomach churned only the slightest, what was this place? It smelled- Itachi could barely describe how badly it smelt, dirty. Unclean, as if he were sat next to the Sandaime as he smoked simply to breathe in the acrid haze.
Only it smelt a hundred times stronger, permeating the air. Glancing around carefully Itachi took in how utterly unfamiliar the buildings around him were. Itachi himself was perched on the roof of a grey, blocky and tall building, reaching as high as the buildings he remembered in Kumogakure. Even so, Itachi remembered Kumo having so much more life in their architecture, so much more "design" and all of this just seemed to be metal, stone and glass.
Lifeless.
Splotches of green caught his attention every so often, but they were splashes of colour- tiny parks, with patchy grass and a spattering of trees here and there.
This was so different from what Itachi'd ever seen, this city sprawled further than he could even see, buildings fading into the distance out of his range of perception. But it all looked the same, different heights and lengths or rotations of the same things. Splashes of differentiation here and there but even the differences tended to have duplicates.
It all looked so mass-produced. Though, Itachi admitted- there were a few unique places, more popular than the rest- obviously places of interest though. Not even Kirigakure was as dull as this place. It was just dreary and deplorable there.
But as he watched the civilians ( Because that was all he could believe them to be, as he watched the masses go about their daily life blissfully ignorant of anyone able to turn around and open their throat with a blade at any moment. ) Itachi could tell if he asked someone where this was, he would most definitely get an answer that did not pertain to the Hidden Continent.
Itachi supposed that was fine. He had come to terms with everything he had wanted to accomplish with his 'last life'.
What Itachi had not come to terms with, was what was actually going on. Questions poured through his head as he sat there overlooking it all.
Why was he alive?
How was he alive?
What had happened to his world?
Sasuke, Naruto, how were they? Were they dead? Alive?
No, he couldn't dwell on it. Itachi had died in that world, and when he was dead he had been content with where he had left the Shinobi World. Just because he had been revived, didn't mean he could go back and start worrying about people who would most likely...
Never be seen again.
Itachi sighed, a quiet, but long exhale of breath to shake the darkening thoughts from his mind. Standing up from where he was crouched, her tilted his head to look for a less startling way to get down from the building he was perched upon.
He sighed, glancing down at his clothes. Odd...a dark grey shirt and black, slightly tight pants with strangely designed but slightly comfortable civilian shoes. Itachi sighs, he supposes it's better than being naked.
But Itachi is pretty sure he's unarmed, and while that isn't a problem, because Itachi can think of at least ten ways to disembowel someone with a smashed teacup- it's not as if he's going to have a problem finding weapons to use. It's still a little vexing to be in an unfamiliar area with no weaponry to speak of- Itachi feels like he's walking back into Konoha with throat bared and a sheet of silk to cover himself.
That is to say, completely out of his element.
He gives up with finding a "normal" way down, simply shunshinning into an alleyway he can spot from his higher altitude. He turns to leave the alleyway, but stops short.
Rip, sniff, tear, spllcchh-
He can smell something- it smells like the best food he can't think of, and he turns, frowning. Whatever someone was eating. It wasn't food. And as Itachi turns, to look, his eyes widen just slightly.
Someone's hunched over a corpse, muscle being torn from the still figure by the one above them. Blood leaks through the eating one's fingers, and splatters the ground. It's... it's human blood, that's-
Itachi can only give credit to the countless brutal killings Kisame performed that he did not outwardly express his abrupt nausea.
The thing hunched over the corpse pauses in its eating, looking through dark, matted tresses with black and red eyes to stare at Itachi.
"This one's mine, sorry... I-" The woman looks down at the corpse, and sighs. "I haven't eaten in a few months... but are you hungry, dear?" Itachi slips closer, mind racing, and the woman smiles hesitantly, going back to rip the lower part of the left arm from the body. "I can probably spare this much, you look just as starved as I do."
Itachi stared at the arm, tilting his head- how was he supposed to react to this? His stomach churned with hunger, and against his will he could feel his mouth start to salivate.
The woman tilted her head in response, peering at him in confusion. "What's wrong?" She seemed to pause, before blinking in surprise. "Are you... are you new here? Sorry, you should probably go see Anteiku then... They should help you sort out some hunting grounds- but for the time being... here."
Itachi watched silently as she folded the corpse up and slid it carefully under a dumpster near the end of the alleyway, taking some rubbish and half empty food bags and stuffing them with it. She clapped her hands together as if to wipe away some invisible grime off her bloody fingers and turned to him, smiling.
"Come on now, I'll take you to Yoshimura-san, he'll know what to do." She said, rushing forwards to grab Itachi's forearm, tugging him along as she led him through a series of contrived alleyways. "What ward did you come from? I'm from the Nineteenth myself, not as friendly as this one, but close. Oh, my name's Anzu- Ironic, hmm? I'm named after a fruit I can't eat." Anzu murmured, filling the silence between them, and Itachi couldn't help but stare at the odd mix of somber and friendly cannibal.
What... what was going on exactly? Itachi couldn't really tell, but it was better than having to kill someone- already. So soon after he came back to life.
Anzu slid to a stop in front of two oddly dressed teenagers, one male with short black hair and an eyepatch who looked as if he could've fainted at the sight of Itachi's cold expression. The other was a girl, shorter than the male with a dark bob, glaring at Kaneki before glancing at Anzu and Itachi with a skeptical facial expression.
"What do you want, Ichiro?" Itachi almost rose a brow at the immediately hostile tone of the girl.
Anzu hummed, grinning slightly at Touka. "Newbie on the block, bringing him to Yoshimura-san That's alright... right, Touka?" The boy looked even more nervous when 'Touka's eyes darkened with rage.
"Get out of here, I'll take the new guy up to the manager." Touka hissed, and Anzu started to laugh, waving Itachi goodbye as she slunk off.
Turning to Itachi, she grimaced, kicking the boy in the shins and shoving the trash bag that was left at her feet into his hands. The boy squeaked in pain, almost falling to his knees. "Go put that in the dumpster while I sort this out, idiot- remember, black top is general waste, blue is recylcling."
"A-aal-right Touka-san!" Was the reply, and Touka tilted her head to give Itachi a quick stare.
Itachi sighed, and as he walked past the shorter male, gave him a slightly sympathetic glance.
Whatever was going on, he had better adapt quickly.
"What is my purpose and my position? Where do I go? Where can I go? I'm well aware that my entire life has been a one giant lie."
Itachi's eyes shut briefly, and as he followed the girl into whatever his next stage of life was, Itachi could only hope there was to be some honesty to be had in this world. For the lies he had swathed himself before his death left him tasting foul flavours in the back of his throat.