The sun hung low over the ghost town of City Z, casting long, skeletal shadows across the cracked pavement. For most, this was a death trap of monsters and urban decay. For Jack, it was home—and the ultimate training ground.
## The Long Grind: Three Years of Hell
When Jack first arrived in this world, he knew the clock was ticking. He didn't seek out the Hero Association or try to find a Master. He went straight to the source of absolute power: a man with a full head of hair and a mediocre suit named Saitama.
The next three years were a blur of agony. Jack didn't just train *with* Saitama; he lived his shadow.
* **The Daily Hell:** 100 push-ups, 100 sit-ups, 100 squats, and a 10km run. Every. Single. Day.
* **The Mental Fortitude:** No air conditioning in the summer, no heat in the winter.
* **The Bond:** They shared lukewarm hotpot, fought over grocery store coupons, and fended off low-level monsters that dared to interrupt their cheap dinners.
By the second year, Jack's muscles weren't just toned; they felt like they were being replaced by high-tension steel cables. But the human body has a ceiling. Jack knew that to keep pace with the man who was shattering his "Limiter," he needed a catalyst.
---
## The System Awakening
Three months into the journey, the **Crafting System** chimed in his mind. It wasn't a "Level Up" system; it was a cosmic laboratory.
While Saitama was napping after a particularly grueling session, Jack carefully collected a single drop of blood from a scrape Saitama had earned (back when he could still bleed). The result was the **Saitama Serum**.
> **Saitama Serum [Grade: ???]**
> *"The physical embodiment of a broken ceiling. Side effects include total follicular exodus."*
Jack drank it without hesitation. He felt his DNA scream as it was rewritten, his potential expanding into an infinite void. As predicted, his hair began to fall out in clumps within weeks. By the end of year three, both men stood atop their apartment building, two shining beacons of baldness overlooking the ruins of City Z.
---
## The "Friendly" Visit to House of Evolution
Jack was strong—absurdly so—but he wasn't satisfied with just being "Saitama Lite." He wanted versatility. This led him to the doorstep of the **House of Evolution**.
The "discussion" with **Dr. Genus** was brief. After Jack effortlessly punched through a dozen clones and caught Carnage Kabuto's horn with two fingers, Genus became remarkably cooperative. Jack didn't want the throne; he wanted the data.
The System ingested decades of Genus's forbidden research in seconds.
* **Genetic Mapping:** Uploaded.
* **Cellular Regeneration:** Mastered.
* **Monsterification Mechanics:** Decoded.
---
## The Hair Miracle and the Collector's Path
The first order of business was vanity. Using the biological data, Jack crafted two vials of **Hyper-Follicle Restoration Essence**.
Saitama, mourning the loss of his favorite shampoo, didn't even ask what was in the needle. Within minutes of the injection, Saitama's head erupted in a thick, lustrous mane that looked like it belonged in a high-end hair commercial.
"Jack," Saitama said, staring into a cracked mirror with tears in his eyes, "You're a god."
But Jack's true work was just beginning. He began to move through the shadows of the hero and monster worlds alike:
* A stray hair from **Silver Fang's** dojo.
* A drop of blood from a battlefield where **Tatsumaki** had been grazed.
* Scrapings from the armor of **Boros** (eventually).
By combining his broken Limiter with the genetic blueprints of the world's strongest entities, Jack wasn't just becoming a hero. He was becoming an **Apex Creator**, capable of crafting items and serums that could turn a pebble into a tactical nuke or a human into a god.
Saitama had the strength to end any fight with one punch. Jack was building the power to rewrite the world itself.
The air outside the Hero Testing Center was thick with the smell of sweat and the sound of Saitama grumbling about the written exam. Jack, sporting his newly restored hair and a physique that hummed with untapped kinetic energy, was about to offer some comfort when the world blurred.
A translucent, neon-blue screen flickered into existence, hovering inches from his nose.
---
### **[Interdimensional Chat Group]**
**System:** *Welcome, user 'Jack', to the Multiverse Hub.*
**Status:** *Connected.*
* **Momonga (Admin)**
* **Tony Stark**
* **Jack**
---
Jack paused, his hand still mid-air. Saitama kept walking, oblivious. "Hey, Jack, you coming? I think I barely passed. That essay on 'Justice' was a real pain."
"Yeah... give me a sec, Saitama," Jack muttered, his eyes scanning the flickering text.
The interface was sleek, far more advanced than his own Crafting System's utilitarian menus. Before he could even process the implications, the chat feed began to scroll.
---
**Momonga (Admin):** Another one? This makes three. I was beginning to think I was trapped in a broken dev-room.
**Tony Stark:** 'Momonga'? That's either a very dedicated cosplayer or I've finally had a stroke. And who's the new guy? 'Jack'? Very original. Please tell me you have a last name and a basic understanding of physics.
**Momonga (Admin):** Be silent, Stark. My magical sensors—or whatever passes for them in this interface—suggest the newcomer possesses a presence that... frankly, makes your Arc Reactor look like a AA battery.
**Tony Stark:** Ouch. Rude. Though, he isn't saying much. Hey, New Guy. If you're currently being abducted by aliens, blink twice. If you're a god, please keep the lightning to a minimum. I just polished the floors.
---
Jack felt a smirk tugging at his lips. He looked at Saitama's back—the man who had just broken every physical record in the Association's history—and then back at the screen.
He had the **Saitama Serum** coursing through his veins, the biological genius of **Dr. Genus** in his brain, and a **Crafting System** that could turn a billionaire's tech into scrap metal.
He began to type.
**Jack:** Physics is more of a suggestion where I live, Tony. And Momonga... if you're the guy I think you are, don't worry about the 'dev-room.' The world is much bigger than an MMO.
**Tony Stark:** Great. Another cryptic powerhouse. Just what my ego needed.
**Momonga (Admin):** Interesting. You seem to know of me, Jack? That shouldn't be possible. Perhaps this group is more than just a random connection of souls.
---
Jack watched as the icons pulsed. He realized his "collection" was no longer limited to the genetic materials of City Z. With Tony Stark's mechanical brilliance and Momonga's magical artifacts potentially on the table, his Crafting System was about to go into overdrive.
"Jack! Come on! The grocery sale ends in ten minutes!" Saitama yelled from down the street.
**Jack:** Hold that thought, guys. I have to go help the strongest man alive carry eggs.
**Tony Stark:** ...Eggs?
**Momonga (Admin):** A humble pursuit. I shall await your return. We have much to discuss regarding the 'nature' of our respective worlds.
Over the next week, the chat group became Jack's primary source of entertainment during the quiet lulls in City Z. Between Saitama's mindless TV watching and their occasional monster-hunting strolls, Jack was busy navigating the egos of a paranoid Overlord and a snarky billionaire.
He played his cards close to his chest. No mention of "Overlord" light novels or Marvel movies. To them, he was simply an inhabitant of a chaotic, high-power-scale Earth.
---
### **The Interdimensional Exchange**
**Tony Stark:** So, let me get this straight. You have a "Hero Association" that ranks people from C to S? And your neighbor—the egg guy—is essentially a walking extinction-level event, but the bureaucrats think he's a fluke?
**Jack:** Pretty much. The system here is obsessed with flashy aesthetics and public popularity. Saitama just... lacks the branding. But in terms of raw output, I've seen him split the clouds with the shockwave of a casual punch.
**Momonga (Admin):** Cloud-splitting through sheer physical force... that would require a Tier 10 strength stat or a World Level Item. This world of yours, Jack, it seems dangerously unoptimized. How do the "Monsters" function? Are they summoned? Spontaneous generation?
**Jack:** It's a mix. Some are biological experiments gone wrong, some are aliens, and others are just humans who obsessed over something so hard they literally transformed. I call it "Monsterification."
**Tony Stark:** Obsession leading to physical mutation? Note to self: stop spending 72 hours straight in the workshop. I don't want to turn into a giant wrench.
---
### **The "Gifts" and Hidden Motives**
Jack wasn't just chatting for the sake of friendship. He was gauging the **system's integration**. He discovered that the chat group had a "Point" system and a "Transfer" function.
While Momonga talked about the struggles of managing the Great Tomb of Nazarick (referring to it only as his "organization"), and Tony complained about the lack of decent coffee in his lab, Jack began to feed the **Crafting System** the concepts they discussed.
* **Analyzing Stark's "Repulsor" theory:** Even without the blueprints, Jack's biology-focused mind began to wonder if he could craft a "Repulsor Organ" using the genetic data of some energy-projecting monsters.
* **Analyzing Momonga's "Mana":** Jack began to wonder if he could synthesize a serum that granted a "Mana Circulatory System" by studying the biological structure of City Z's weirder supernatural threats.
---
### **A Tense Moment**
**Momonga (Admin):** Jack, you mentioned you "exchanged" words with a scientist recently to gain biological knowledge. Your methods seem... efficient. I find that commendable. Most in my world are blinded by petty morality.
**Jack:** I'm not a villain, Momonga. But I'm not a martyr either. In a world where a giant lizard can step on your house because it had a bad day, you either have the power to say "no," or you don't.
**Tony Stark:** Spoken like someone who's seen some things. Look, if things get hairy in "City Z," I might be able to send over some drone specs. Though, frankly, if your neighbor is as strong as you say, my tech might just be expensive paperweights.
**Jack:** I appreciate it, Tony. Actually, I might have something to send you guys soon. A little "biological booster" I've been working on. No side effects—mostly.
**Tony Stark:** "Mostly" is a terrifying word, Jack.
**Jack:** (Smiling at his screen) Don't worry. I've already tested it on the strongest man in my world. He's never looked better.
---
As Jack closed the panel, he looked over at Saitama, who was currently struggling to open a stubborn bag of potato chips. The "S-Class" exam results were due any day now, and with the chat group expanding his horizons, Jack felt the itch to go out and collect more "raw materials."
Genos, the cyborg, would be arriving soon. And a cyborg's components—combined with Stark's logic—would be a goldmine for the Crafting System.
"Hey, Saitama," Jack called out. "If a blond kid with robot arms shows up asking for an apprenticeship, let me talk to him first, okay?"
"Sure, whatever," Saitama muttered, finally popping the bag open. "You want a chip?"
"Keep 'em," Jack replied, eyes glinting. "I'm going to go see if I can craft something that makes Tony's suit look like a toaster."
The addition of the **Travel Function** changed the stakes entirely. It was no longer just a digital exchange of ideas; it was a potential bridge for cross-dimensional power-leveling. Jack looked at the rules, his eyes lingering on the "combat" restriction. It was a classic balancing act—no "easy outs" if you bit off more than you could chew.
---
### **The Chat Reaction**
**Tony Stark:** Travel? Actual, physical, space-time folding? I've been trying to solve the bridge between dimensions for years, and this thing just hands it out like a participation trophy?
**Momonga (Admin):** Be cautious, Stark. This is a double-edged sword. While it offers an escape or a meeting place, the restriction regarding "combat" is grave. In my world, a battle can last for days or be decided in a millisecond. If you are cornered, there is no retreating through the screen.
**Jack:** It's a fair trade. No coward's exit. Besides, I don't think any of us are looking to run away.
**Tony Stark:** Speak for yourself, Jack. I like my heart where it is—inside my chest and not on the end of a monster's claw. But... I'd be lying if I said I wasn't curious about that "Saitama" guy. Is he really just a guy who did too many squats?
**Jack:** Seeing is believing, Tony. But maybe wait until he's not in a bad mood about the supermarket sales.
---
### **The Collector's Strategy**
Jack leaned back on his balcony, looking out over the desolate skyline of City Z. The travel function opened up a terrifyingly efficient possibility for his **Crafting System**.
1. **The Marvel Buffet:** Tony's world was a goldmine of exotic materials. Vibranium, Uru metal, Extremis, and even the unique biology of "Supers." If Jack could get a sample of Steve Rogers' blood or a shard of Iron Man's gold-titanium alloy, his crafting options would skyrocket.
2. **The Magic Library:** Momonga (Ainz Ooal Gown) sat on a mountain of Tier-based magic items and YGGDRASIL data. Jack's system had already assimilated Dr. Genus's biology; what would happen if it assimilated the logic of a **World Level Item** or an **Elder Lich's** mana core?
---
### **Testing the Waters**
**Jack:** Momonga, that "organization" of yours. Do you have any discarded materials? Broken armor, spent scrolls, or even just samples of your world's unique flora?
**Momonga (Admin):** I have vaults filled with what I consider "trash" from the perspective of my guild. To you, they might be artifacts. Why do you ask?
**Jack:** I'm a... creator of sorts. I can refine things. I'll make you a deal: send me some "junk" through the transfer function, and I'll send you back something your world has never seen. A fusion of science and raw power.
**Tony Stark:** Hey, don't leave the genius out. Jack, if you can get your hands on some of that "Monster" tissue you mentioned—the stuff that causes the rapid mutation—I'll trade you some Clean Energy blueprints. I want to see if I can stabilize it without the "turning into a giant crab" part.
**Jack:** Deal.
---
### **The Arrival of the Student**
As Jack finished typing, a loud *boom* echoed from the street below, followed by the mechanical whirring of turbines. He looked down to see a young man with blonde spiky hair and black-and-gold cybernetic arms standing in the crater of a destroyed building.
**Genos** had arrived.
Jack smiled, the blue light of the chat panel reflecting in his eyes.
"Saitama! Your fan club is here!" he shouted toward the apartment.
Then, he sent one last message to the group.
**Jack:** Hang tight, guys. I'm about to collect some high-end scrap metal. I'll see if I can send you a "care package" soon.
With a flick of his wrist, Jack closed the panel. He didn't just see a hero-in-training down there; he saw the next evolution of his Crafting System. Between Stark's tech, Momonga's magic, and Genos's hardware, Jack was about to become the most versatile "monster" the world of One Punch Man had ever seen.
The items were no longer the stuff of myths, but practical, iterative steps in a grander experiment. Jack sat on his tattered sofa, watching the "Processing" bar on his system flicker. He wasn't trying to build gods yet—he was trying to build tools that worked.
---
### **The Technical Trade: Refined Materials**
**Tony Stark:** Alright, I've looked at those "Monster Carapace" fragments you sent, Jack. The carbon lattice is impressive, but brittle. I ran them through a molecular press with some aerospace-grade titanium.
**Jack:** What's the verdict?
**Tony Stark:** I'm sending you the **[Experimental Alloy Mesh]**. It's not a suit, just a few square feet of material. It's got high tensile strength and heat resistance. Good for reinforcements, but don't expect it to stop a tank.
**Jack:** Perfect for a base layer. In return, I'm sending **[Concentrated Adrenaline Vials]**. I refined these from various biological samples. They won't make you a superhero, Tony, but they'll keep you awake and focused during a 48-hour crunch without the caffeine jitters or the heart palpitations.
**Tony Stark:** I'll take the "no heart palpitations" over a new suit any day.
---
### **The Arcane Trade: Raw Energy**
**Momonga (Admin):** Jack, the "discarded materials" you requested have been dispatched. I have included several **[Faded Mana Crystals]**. Their energy is nearly depleted and unstable for high-tier spellcasting, but they should suffice for your "refining" process.
**Jack:** I see them. They're buzzing. What's the catch?
**Momonga (Admin):** They are volatile. If handled incorrectly, they will simply shatter. I am curious if your world's "physics" can contain "Magic" in its rawest, most degraded form.
---
### **The Crafting Result: The Hybrid Prototype**
Jack fed the **Alloy Mesh**, the **Faded Crystals**, and a small sample of his own blood—thinned and diluted—into the Crafting System. He wasn't aiming for "Legendary" gear; he was aiming for a proof of concept.
**Jack:** Sent the results to your private stashes. Check out the **[Integrated Weaver's Patch]**.
> **Item:** [Integrated Weaver's Patch]
> **Grade:** Uncommon (Experimental)
> **Description:** A small, adhesive patch of reinforced alloy infused with a trace amount of mana.
> * **Stark Component:** Provides localized structural reinforcement to whatever it's stuck to.
> * **Momonga Component:** Slowly absorbs ambient thermal energy to maintain a low-level "Hardening" effect.
> * **The Jack Factor:** Uses biological data to ensure the patch doesn't reject the wearer's skin.
**Tony Stark:** A smart-bandage? It's a bit low-tech for me, but the way it draws heat from the environment to toughen up the alloy... that's a clever bit of thermal dynamics I hadn't considered.
**Momonga (Admin):** To think you could stabilize mana within a non-magical metal using nothing but biological "glue." It is a crude item, but the logic behind it is... intriguing. It is a bridge between two incompatible systems.
---
### **The "Care Package" for the Student**
**Jack:** Tony, I need a favor. I'm looking at those **[Mark IV Power Core Schematics]** you sent earlier. I'm going to try and strip them down.
**Tony Stark:** Strip them down? Those are state-of-the-art.
**Jack:** My "student" Genos is essentially a walking furnace. If I can use your cooling logic and Momonga's energy-stabilization crystals, I can give him a core that doesn't overheat every time he uses his maximum output.
**Tony Stark:** Fine. Just keep the data encrypted. I don't need a teenage cyborg in another dimension leaking my patents.
Jack closed the window as a shadow fell over the balcony. Genos was standing there, his metallic eyes whirring as they scanned Jack.
"I am here to see Sensei Saitama," Genos stated flatly. "And you... you possess a strange energy signature. It is biological, yet it lacks the usual human limitations."
Jack grinned, sliding a small, glowing vial into his pocket. "Saitama's inside, kid. But if you want to stop blowing your arms off every time you fight a mosquito, we should talk."
Genos stood on the balcony, his sensors clicking as they struggled to categorize Jack. To the cyborg, Saitama was an anomaly of pure power, but Jack was something else entirely—a shifting mosaic of biological signals and strange, low-level energy hums that shouldn't exist in a human body.