A demon's guide

As his world darkens, instead of fear and regret, a swell of happiness swells up in him, his thoughts being consumed by his past all he did right, all he did wrong, all his suffering, all his joy, all these flashes through his mind, yet what lingers in his consciousness is the joy of finally taking his last breath, he has been seeking his death ever since he was kidnapped as a kid and taken to a weird warehouse facility where they were trained to be killers, he was not the brightest, not the strongest, but in the end it doesn't matter, because at the end of the day he is the one who lasted, he's the one who escaped, the one who hunted. After years of this torturous life, he has succeeded in killing every single one who killed his family and the ones who managed the facility.

Time passes infinitely long when you're dead, not knowing where you're going, only knowing that you're moving, having none of his basic senses, only feeling motion, until one day, bright light shines upon him, his senses coming back, he found himself sat upon a comfy sofa, a guy wearing a suit and tie with a mountain of paperwork in front of him, and when he's about to speak, he felt himself falling, his surroundings again darkens, as his senses went back to before.

This time, when he woke up, he found himself surrounded by wreckage, rotting corpses littered around him, not knowing what to do, he first hid himself, trying to know what is really going on, he crouched low, slipping into houses, after a whole day of scouting, he found out that he's the only person in this place, he also noticed that his body is in fact not his body, this made him think that he's been reincarnated, after confirming that he's the only living person in the village, he then walked into the largest building at the center of the village, he started by gathering all the scrolls, books, weapons and parchments in one place, and when he opened one of the scrolls, a splitting headache erupts, flashes of memories, knowledge, experiences that he has never had came rushing back in him, memories of a person named an Ichigo Uzumaki rushes at the forefront, knowledge and experience of swordsmanship, Fuuinjutsu, Ninjutsu, what his hobbies were, what he did for dinner that day, and how he died, then another set of memories came crashing in, memories of an Ichigo Kurosaki, of how he became a shinigami, how he defeated Aizen, Yhwach, Hell, he remembers studying in medicine, how even after he became a doctor of his clinic, he still continues his studies of Kidos, and Zanjutsu and continue to work as a Shinigami, his memory of Shiro, Zangetsu, Yoruichi, Inoue, and especially his son Kazui, etched in his mind, overloaded by the information, Ichigo fell into unconciousness, the scroll in his hands accompanies him as he fell to the ground.

Days passed since that memorable experience, he found out the hard way, that the energy of this world is not the same as the reiatsu he used to know, after careful examination, he noticed some subtle differences between them, unlike the energy called reiatsu that he knows, Chakra is more malleable, more flexible, but it is also harder too control, he even tried to use techniques from his 1st incarnation only blow up in his face literally, even using Shunpo almost cost him his leg, from that day onwards he has started experimenting on how to use his kido techniques with chakra.

Experiments have their ups and downs, the upside is he found out his current body has some kind of regeneration ability, and the downside is he found out his body has a regeneration ability, now it suffices to say that pain has been a constant part of both his past incarnation, but breaking your bones or mutilating your body multiple times just to see if you can use such techniques can and will affect a person's mentality, whether they be for good or not, depends.

wondering the vast land, as he searches for any other of his kind, he remember that under the Kage building resides a monster that no one can kill, it's so strong that the 1st Uzumaki has to give his life just to seal it, so there he went, as he breaks open all the trapdoors, unseal all the trap seals, he found himself face to face to a massive beast of huge proportion, there with its eyes closed laying in peace is a four-legged dark scaled drake, its horns bending to the side then protruding forward, it's scale glistening under the light of his torch, it's not fear nor shock that's gripped his heart but familiarity and confusion, he knows this beast, its name rolling through his tongue as he mutters "Zangetsu??", hearing his voice the beast opens his eyes, deep golden iris stares back to the cerulean blue of the man in front of him, confusion on his face, the beast mutters back "Ichigo?", hearing the beast's answer, he walks up to his friend only to be shocked and hurled backward by an invisible force, laying on the floor his eyes noticed the seal on the sealing caging his friend from his past incarnation.

"How??" asked Ichigo as he sat up from his vertical position, his voice trembling with cheer, confusion, and realization, he then tried to tap into his soul like how he's done it in his past life only for nothing to happen, Zangetsu watches him with both amusement and care as he said "It won't work, the laws of this world are different from where we came from, this world's energy is different from our earth, in this world there's no Seireitei, no Hueco Mundo, no Hell, but guess what this world has,...…. aliens" his smirk widening as he watches Ichigo's face look back at him, "How do we go back then? last thing I remember is my soul being split apart after I die," Zangetsu's face turn into a frown when he heard that, "I know, I was there, the reason we were split was because we're two beings but occupy the same soul and body, now someone up there," he said as he pointed his claws upward "doesn't like that, so your soul was split into two, i've been here way longer than you, a few eons maybe, I'm not sure, the first thing I remember is waking up by a tree filled with this world's energy, then this white lady with scary white eyes tried to kill me, I got lucky when this lady's attention was caught when someone called her or else I might not be able to even escape, then for a few centuries, I just wander around, i even learned to harness this energy, it's tamer than a hollow's energy so it's easy to shape it, then a few centuries later others like me was popping out of nowhere, at first they're not doing anything, just being annoying or just going around terrorising some settlements, but one day i saw these people with red-hair starts hunting us down, then they seal us in humans, only the fox and i can't be sealed in humans, their body began to decay, then in a few weeks they die, all of my host died in a matter of a few days," Ichigo listening silently scruffed his eyebrows, understanding what he just said, "So what are you gonna do after you're out?" he looks back to Zangetsu as he starts drawing counter seals to disable the cage, "If it's alright with you, I wanna be in you again." he said with a warm smile, Ichigo turned his head back to Zangetsu so fast his head might have flown off, disgust written on his face, "Not like that you moron, seal me in you, you're an Uzumaki in this life aren't you?? Uzumakis are the only ones who can handle Bijuu chakra. You fucking imbecile!!" his clawed hands slapping his forehead as he sighs noticing that his friend's idiocy might not be a problem with his blood but his soul, his very essence is just that dumb "Uh, sure, but are you sure you don't want to live freely?" Ichigo asks as he draws the last line of the counter seal, "You've been locked up for who knows how many millenia." he continued, jumping down from the ceiling, his feet landing in mid air as he glides downward, controlling his chakra with perfect accuracy, "And I've also lived freely for many millennia, I might even outlive you in this life, so it's alright if i spent the next century with my bestfriend, so King, what do you say, let's kick some ass again." hearing his partner say so, he decided to accept his offer, after cancelling the gate, he then walks back up to the surface, scrounge his pile of books about Bijuu sealing techniques,there he finds out about the eight trigrams sealing techniques and researched a way to not constrict the bijuu, so with a new and reformed seal, he went back to Zangetsu, and summoned his chains and used them to draw the seals on his back, after drawing the primary seal, he used his chains and bound Zangetsu within them as he pulls him inwards, sucking Zangetsu to the seal "Don't worry buddy, you can come out whenever you want, I left the gate open, though I'll be siphoning part of your Chakra into mine, in this life you're gonna pay rent." he jokingly said inwardly, as he felt part of his Chakra slowly merging with part of Zangetsu's.