Regressed with Omnipotent AI on Zombie Apocalypse(FF)

A young man with black hair crouched behind a door, peering through the narrow gap. He could see the pale figure of something—or someone—approaching him. His heartbeat pounded, quickening with each step it took closer. He glanced around and grabbed a bat lying nearby, clutching it tightly.

The creature was coming, and he knew there was no way to avoid it. Running past it wouldn't help; more would likely follow. He swallowed hard, bracing himself as he waited for it to enter. The footsteps echoed in his ears, each one a grim warning. Taking a deep breath, he steeled himself, and as the door began to creak open, he swung the bat with all his strength.

The bat struck the pale figure square in the chest, crushing its ribs. Blood sprayed across the floor, splattering onto him, and he fell to his knees in shock, staring at his attacker. Just a few hours ago, this creature had been his neighbor. They hadn't been close, but they'd always exchanged a smile and a nod whenever they passed in the hallway.

"Is it… is it over?" he gasped, his breath coming in heavy pants.

But it wasn't. The creature let out a guttural growl and clawed its way across the floor toward him, its fingers digging deep into the tile. He froze, eyes wide with panic, but adrenaline surged through him, clearing his mind of hesitation. This wasn't his neighbor anymore; it was a monster. Life or death. He gripped the bat tighter, raised it, and slammed it down on its head again and again.

Sweat dripped from his forehead as he kept swinging, not stopping until the creature finally lay still. Breathing heavily, he allowed himself a sigh of relief. But just as he thought it was over, pain exploded in his neck. He felt himself yanked backward, powerful hands grabbing him from behind.

"Arrgh!" he screamed, the agony overwhelming him as his life slipped away.

Zack jolted awake, gasping, his eyes wide in shock as he looked down at his hands, flexing his fingers in disbelief. "Wasn't I eaten by a zombie? How… how am I still alive!?"

Suddenly, he remembered something and glanced frantically at the calendar on the wall.

December 13th, The Corona virus Zeta variant had broken out two days ago, transforming 80% of humanity into mindless, flesh-craving zombies overnight. Civilization had collapsed instantly, like the switch of a light.

Though Zack was one of the lucky 20% who survived, his fortune hadn't lasted. Just two days later, zombies had broken into his apartment, and he had joined the ranks of the undead himself.

"Did I… get a second chance?"

Zack forced himself to calm down, piecing things together. He had been reborn.

A wave of shock washed over him as he stumbled to the window, peering out at the street below. It was a sight he'd never forget—ruined streets littered with debris, thick smoke pouring from shattered buildings, cars smashed into each other, and a vast, staggering horde of zombies aimlessly wandering the streets. They staggered in every direction, groaning mindlessly as they clashed with one another.

On the street below, he recognized some of the zombies gathered around the building entrance—they were once the familiar faces of his neighbors. These very same zombies had broken into his apartment last time and ended his life.

"No way am I letting that happen again!"

His face hardened with determination as he yanked a dusty baseball bat from under his bed. Digging around, he found a few nails and hammered them into the bat's head, creating a crude but deadly mace.

As he tightened his grip on the bat, his fear started to fade. He was done waiting around to die. This time, he would fight back.

Just as he reached for the door, a calm, mechanical voice sounded in his head.

"Sir, if you proceed outside now, your chances of survival are nearly zero."

Zack froze, his grip tightening on the bat. "Who… who's there?!"

"Sir, I am your intelligent assistant, Ego."

The voice sounded real, but the flat, synthesized tone betrayed its artificial nature.

"Ego…?" Zack whispered, the name sparking recognition. "Wait a second… Are you Tony Stark's AI butler from Iron Man?"

"No Sir, Copyright God will surely smash this world if that is the case. I am your intelligent assistant, dedicated to serving you above all others."

"Hold on a minute… let me catch my breath."

Zack took a deep breath, struggling to process what he was hearing. His mind reeled as he remembered a classic rule from the novels he loved—regressed mc often had a cheat-like advantage, some kind of "system" to help them survive. 

"Guess mine is… Ego?" he muttered, half in disbelief.

He sighed, a bit disappointed. After all, Ego was an AI, not a fighter. It's not like Ego could physically help him fend off zombies. But he couldn't afford to waste time.

"So, Ego… what exactly can you do?"

"Sir, I am equipped to assist in your survival. After analyzing the area, I've identified 18 ways to create effective weapons from available resources. I suggest making an air nail gun, fertilizer bombs, Molotov cocktails, and bait to improve your odds."

Ego then listed the items he'd need, even marking their exact locations around the apartment.

"A fertilizer bomb?" Zack repeated, blinking in surprise. "Wait… sodium nitrate. I get it now!"

In the midst of what seemed like a hopeless situation, Zack suddenly saw new possibilities. Survival might be possible, as long he follow Ego suggestion.

Fueled by newfound resolve, Zack quickly gathered the materials scattered around his apartment. There were fire extinguishers, alcohol, a few smoke alarms, AA batteries, aluminum cans, and even a half-bag of fertilizer left by the previous tenant.

Some of the items needed a bit of dismantling.

"Sir, please unscrew the front panel of the air conditioner, and use the screwdriver to your right to turn counterclockwise," Ego instructed in his usual calm voice.

"Ego, do you think I'm clueless?" Zack grumbled while prying open the air conditioner. "I know which way to turn a screw."

"Understood, sir."

With Ego's instructions, Zack carefully assembled the makeshift nail gun. The main component was a modified fire extinguisher, the barrel was crafted from copper piping in the air conditioner, and the nails served as makeshift bullets.

It looked crude, but it was complete.

"Will this really work?" Zack mumbled, a hint of doubt in his eyes. He pointed the nail gun at the wall and pulled the wooden trigger.

Bang!

The screws burst out, embedding deep into the wall and leaving a visible dent.

"Whoa! That's… incredible!" he gasped, wide-eyed. This thing was as powerful as a pistol, yet it barely made any noise. It was the perfect zombie-killing weapon.

"Sir, be aware that the nail gun's power depends on the pressure in the fire extinguisher. After about eight shots, it will lose it's effectiveness."

"Noted," Zack replied, nodding. He couldn't expect miracles from an improvised weapon, but its power had already exceeded his expectations.

"So, Ego," he asked, brimming with curiosity while preparing the fertilizer bomb, "besides weapon-making, what else can you do?"

"My database includes all kind of data for example Tech weapons, the blueprint for the Zero Point Reactor, blueprints for power armor, and formulas for the Superpower Serum …"

Zack froze mid-step as Ego continued listing off capabilities, each one more mind-blowing than the last. His hands trembled, and a slow smile spread across his face. He remember reading about zero point reactor, it capable to produce energy out of nothing.

It was no exaggeration to say that Ego's database was like a glimpse into the future, a treasure trove of technology easily a hundred years ahead of anything on Earth. Perhaps even centuries ahead. There were nearly a hundred different power armors within it, from normal armor to even one made using nanomachine.

But Zack knew better than to get cocky. He understood that these were just blueprints, information stored in Ego's memory banks. Until he made it out of this apartment alive, they were as good as dreams.

"Ego, let's keep going," Zack said with renewed focus.

"Understood, sir," Ego responded.

Taking a deep breath, Zack resumed assembling the makeshift bombs and incendiaries. Soon enough, he had finished the fertilizer bombs and Molotov cocktails. Only the bait was left.

Just as he was working on the final screws, he heard a loud, frantic banging downstairs, followed by a desperate cry for help.

The voice come from a female, and she was clearly in serious trouble. The sound of wood splintering reached his ears, and he realized the zombies had discovered someone in the apartment below—a female streamer, if he recalled right.

But he knew better than to try and help. Within moments, the sound of her door shattering filled the air, and her scream ended in abrupt silence. Zack tensed. Last time, the zombies had discovered him shortly after breaking into her place. 

"Focus," he muttered to himself, speeding up his work on the bait.

A few minutes later, the device—a crude bait crafted from a smoke alarm—was ready. Holding it tightly, he approached the window and scanned the street. Most of the zombies outside had been attracted by the commotion below, crowding into the hallway around the second-floor apartment.

"Hope this works," he whispered, then hurled the bait out of the window. It landed on the lawn of the building next door with a loud, wailing sound.

The moment the high-pitched sound reached them, the zombies went wild, abandoning their current targets to follow the sound. Even the zombies from the adjacent building began to change direction.

"Sir, you have seventy-five seconds," Ego's voice alerted him calmly.

"Got it." Zack slung his prepared backpack over his shoulder, grabbed the nail gun, and opened his apartment door.