The assassin's blade fell.
But in the nanoinstant between its descent and Sei's complete possession, the system acted.
Time slowed, not literally, but Sei's hijacked nervous system now processed information at inhuman rates. The system flooded his blood with adrenaline, neuroadrenaline and cortisol and his brain with neurotransmitters, forcing synapses to fire in patterns that never existed before. Every unnecessary biological function suppressed to redirect resources towards but one goal: Survival.
In that moment, physiological changes rippled through Sei's dying body.
Neural pathways burnt as the system carved emergency routes into his brain's grey matter, maximising reaction time by burning the reflex circuits over his conscious decision-making. Providing reaction time at the cost of long-term brain health. Muscles received direct electrical stimulation, bypassing the need for a neuromuscular junction and the conversion of electrical signals into chemical signals. The remaining red blood cells' haemoglobin was chemically altered, allowing for more rapid association and dissociation of oxygen.
Blood still poured from his severed shoulder. The X carved into his back still wept crimson. But the body still moved, driven by something far beyond human limitation.
Sei's body, with the system piloting it, moved faster than human comprehension.
To the five assassins, it looked almost fantastical. One moment their target lay dying pathetically in a pool of his own blood. Next, he's stood three metres away and stood up tall despite the catastrophic injuries that should have left him dead long ago.
"Impossible," their leader muttered under breath.
"Incorrect," the thing wearing Sei's skin replied, voice flat and clinical. "More improbable. Current status: critical failure imminent. Blood loss exceeding sustainable thresholds. Internal damage is extensive. Time until collapse: three minutes, forty-two seconds."
It looked down at the stump where a right arm had once been, watching a stream of crimson blood pump out in rhythm with each heartbeat. However, its face showed no pain. No fear. Mere analytical curiosity, a scientist undergoing research.
"Emergency protocols: complete. Motor efficiency increased by forty-seven percent. Pain response suppressed. Adrenal override maximised," it stated coldly, as if reading from a checklist. Combat capability is time-limited. Unacceptable for long-term survival. Immediate resource acquisition required."
The leader moved first, instincts overpowering shock. His blade flashed forward in a thrust that would have pierced Sei's heart had he not been possessed. The body moved with geometric precision. Torso rotation: forty-seven degrees. Minimal displacement. Maximum efficiency. The steel flew past, close enough to part fabric without touching skin.
"Current survival probability: zero-point-three percent," it said to itself conversationally, dodging another slash with micrometres to spare. "Alternative approach required. Updating strategy... Eliminate targets sequentially. Consume biomass. Stabilise the vessel. Recalculating survival probability..."
It moved. Fast.
So fast the leader's eyes couldn't track it. One moment, he stood in front of him somehow effortlessly dodging his slashes. The next he was there, inside the assassin's guard, left hand rigid. His movement effortless and precise. Fingers pierced through the man's carotid artery like a hot knife in butter. Blood sprayed hot across Sei's face as the assassin's scream came as a wet gurgle.
With a savage twist and yank, he ripped out a chunk from the assassin's throat. Arterial spray painted the clearing crimson. The leader collapsed as his hands clutched uselessly at the remains of his neck.
With a swift motion, the thing raised the torn out flesh and bit down.
The remaining assassins stared in disbelieving horror at their leader's twitching corpse. This wasn't possible; it shouldn't have been possible. Their leader had been a fourth-rank Qi Gathering cultivator, not powerful, but more than just trained and experienced. And this child, this dying child especially, had jus-
"F-formation!" one yelled out, voice cracking. "First formation, now!"
With practised precision, they moved, surrounding Sei's body at cardinal points. Whatever demon they had stumbled across, they would end it together.
The thing cocked its head as it licked the blood off its hand. "Interesting. Blood contains residual Qi. Analysing cellular structure..." After a brief pause. "Marginal regenerative compounds detected. Inadequate for complete healing, but-" It looked at the corpse before looking at the four others. "Additional material available."
Sei dropped to a knee beside the throatless assassin. Plunging its left hand into the man's chest with a sickening crack of ribs. Withdrawing from the cavity, dripping with blood, it held his heart.
"Y-you monster!" An assassin screamed, charging forward with a blade raised. "Die!"
The thing bore no attention to the assassin, calmly examining the organ. At the last second, Sei swayed aside, minimal movement with maximum effect. The blade cut through the air past him. Sei's left leg snapped out in a low sweep, shattering the assassin's ankle with an audible crack.
The man fell, clutching at his ankle as he screamed. But before he had the chance to hit the ground, Sei caught him by the hair and slammed his face into the earth. Once. Twice. Thrice. By the fourth impact, the screaming had stopped, replaced by wet crunching.
Then with a slow, deliberate bite, he bit into the heart he'd been holding. Blood running down his chin as it chewed with mechanical efficiency.
"Blood Qi rapidly replenishing," it noted between bites. "Regeneration marginally accelerating. Time until critical failure: six minutes, thirty-eight seconds. Improvement insufficient. Additional resources required."
The remaining three assassins had gone paler beyond paper beneath their masks.
"Retreat!" the second-in-command shouted. "Fa-fall back and-"
But he couldn't finish. Sei's body moved again with the same impossible burst of speed. It appeared inside his guard as well, left fist already in motion. He didn't have particularly lots of power in the strike, but power is only a third of the equation. The other two, speed and technique, he had in heaps and bounds. Hitting the exact weak point in the jaw to split it while sending rattling his brain in his skull.
The assassin's eyes rolled back as his jaw hung limply in two halves. Unconscious long before gravity claimed him.
"Unconscious resources provide superior blood quality, nutrition and Qi wise," the thing observed, kneeling beside the fallen man. "Panic hormones strip most nutritional complexes."
What occurred next would haunt the remaining assassins until the end of their very short lives.
The thing unhinged Sei's mouth, opening impossibly wide, far wider than human anatomy would allow. Tendons creaked. Jaw joints popped and relocated. Then with natural instinct it latched onto the unconscious man's throat like a lamprey, teeth sinking deep into the carotid artery.
Then it drank, with measured pulls, savouring each mouthful like fine wine. The unconscious assassin's skin paled more and more as colour drained from his face, body twitching and spasming as some deep part of him recognised what was happening. Even in unconsciousness.
Finally, the thing released the desiccated corpse and stood tall. Before the terrified eyes of the assassins, Sei's wounds began to close. The X-shaped wound on his back drawing together, edges meeting and sealing with pink scar tissue. The bleeding from his stump of a shoulder slowed to a manageable trickle.
"Current regeneration: twenty-nine percent of baseline," it stated. "Acceptable for immediate survival. Arm regeneration queued for later. Current priority: elimination of remaining threats and securing meditation location."
It turned to the final pair of assassins. Blood covering Sei's mouth and chin, dripping from his fingers, soaked into his tattered rags of clothes. In the moonlight, he looked like a thing that had just managed to claw its way from hell's deepest pit.
"R-run," one whispered.
And they did.
It titled its head, calculating trajectory, speed, and terrain variables. "Probability of successful escape: zero-point-zero-one percent."
It moved with purpose.
The first assassin made it a mere twenty metres before Sei tackled him from behind. Hitting the ground hard, rolling through undergrowth. The assassin screamed, cried, kicked, and fought back, managing to land a solid punch to Sei's face.
The thing didn't blink. It grabbed the assassin's arm, twisting until the elbow bent backwards with a wet pop, and pressed its snake-like mouth to the fountain of oozing blood.
The other assassin managed to make it forty metres before his foot got caught in a root, and he struggled, crawling forward. He scrambled up, drew a knife and prepared for a final stand.
When he turned, Sei stood but ten metres away, watching with predatory, hungry eyes.
"P-please," the assassin begged, knife trembling. "I-I have a family. Children. I wa-was just following orders-"
"Irrelevant," it said coldly and detached. Then, as if attempting to console him, "Your Blood Qi will be utilised efficiently. You will contribute to this vessel's reconstruction. Your death serves a purpose. That is more than most will achieve."
It slowly approached with measured steps. The assassin lunged desperately, aiming for the heart. Sei simply sidestepped before catching his wrist and, with simple leverage mechanics, turned the blade towards the owner.
Sinking it into his gut. Not a killing blow, just a bleeding one.
"Apologies for discomfort. Optimal extraction requires continued cardiac function; it will be brief."
It was not.
Once finished, Sei stood alone in the moonlit clearing, surrounded by the five drained corpses. The wounds over his body all closed into pink scars, even the once fountain of blood from his stump.
But deep inside, far more important changes were taking place.
Sei sat cross-legged in the centre of the carnage and closed his eyes.
Within his skull, neurones began firing in completely new patterns. Synapses formed connections that had never existed before, pathways optimised for Qi circulation and martial arts rather than mundane thought. It carved new neural highways through grey matter, each modification designed to support cultivation techniques no mortal brain was meant to comprehend.
And deeper within his mind, Sei felt his own thought becoming foreign, his brain restructuring around him like a house being demolished and reformed while trapped in the same space.
Bone creaked audibly as mineral deposits reinforced them at atomic levels. The skeleton that had been merely human began transforming into something that could withstand the pressures of high-level cultivation. Bone marrow expanded its production capabilities, preparing to generate the rich blood that would eventually fuel arm regeneration.
His muscles twitched and spasmed as fibres tore and reformed. It wasn't just healing damage; it was rewriting the fundamental composition of Sei's musculature. Fast-twitch and slow-twitch fibres reorganise into new ratios, optimised not for mundane athletic performance but for channelling Qi and martial arts.
This was the most crucial but also most excruciating change. The twelve main meridians and seventy-two lesser meridians that every human possessed were being forcibly expanded, their walls reinforced and their connections optimised. The system was building infrastructure for techniques that would have shredded normal meridians like paper.
And while his consciousness was suppressed and, for the most part, disconnected from his body. Sei still experienced every ounce of pain. His body being unmade and remade, his biology being rewritten, bones grinding and muscles tearing. Neurones burning as new pathways carve through his brain.
But he could only scream soundlessly into the void.
The thing wearing his skin sat motionless in lotus position, breathing in a precise rhythm that drew ambient Qi from the air, earth and death saturating the clearing.
"Primary objective. Reconstruction cycle: ongoing," it stated to itself. "Estimated time until completion: forty-two hours."
A pause.
"Secondary objective. Arm reconstruction via concentrated Blood Qi meditation. With sustained current saturation levels and optimised marrow production, estimated time until completion: forty-seven days of continuous meditation."
Another pause.
"Tertiary objective. Complete vessel optimisation for full system functionality."
A much longer silence.
"Estimated time until completion: five hundred and seventy-six years, three months and four days."
The thing settled deeper into mediation as if satisfied with the results of its calculations as the reconstruction continued its work. Around it, the five corpses cooled under the moonlight.
Deep within the cage of flesh and bone, Sei screamed. And screamed. And screamed some more into the darkness that would hold him for much longer.
But the body sat perfectly still, breathing steadily, as molecular changes rewrote his humanity into something designed for one purpose only.