City Z is safe and sound. There are no monsters to be seen. Even in this wrecked ghost town, a few people are going about their daily lives as if monsters had never existed. Even the birds are smiling.
Saitama is lying on the floor in his apartment reading manga. His face is emotionless. He is wearing an undershirt and some shorts because it's very hot.
Genos is watching the news. He is fidgeting with a utensil. He's wearing his GENOS hoodie.
"Master." Genos says.
"Eh? What's wrong, Genos?" Saitama replies, glancing at Genos.
"Isn't it odd that there haven't been any monsters around for the past six weeks?" Genos replies.
"Uhh...I don't know. I guess." Saitama replies. He sits up and stops reading his manga, staring at Genos—perplexed.
"I haven't gotten any contact from the Hero Association—other than cases where there might've been monsters, but they have been mistaken, for they were only robbers. It seems like the demand for monsters to appear are going up, as the rest of the Heroes are finding themselves—well, bored. But, in the spectrum of things, this is exactly what Agoni wanted: world peace. What do you say, Master? Ironic?" Genos replies.
"I say it's about time I found something to sympathize with them." Saitama says, making his bored face. "But—Genos, I'm pretty sure monsters will start appearing soon enough. No need to worry."
"My data tells me otherwise. Over the past weeks, in all the cities, the monster appearance rate has dropped eighty percent." Genos says, raising his eyebrow.
"What?" Saitama replies, making his worried face.
"Soon enough, that number will reach to ninety and..." Genos starts.
"What the hell! Why am I reading manga!" Saitama says, as he throws his manga book in the air. He is putting on his Hero outfit.
"What are you planning, Master?" Genos replies. He is scratching his blonde hair.
"Uhh...I'm going out for a stroll...don't follow me. If you do, I'll...uhh...I'll make you clean the bathroom again. You're free to stay here if you want." Saitama says, doing his death stare. He is walking out of the apartment.
"I understand...Master." Genos says, looking down.
Genos watches Saitama as he slams the apartment door shut.
Genos (head): This is my chance to get more intel on Master's great power. Surely, he will not know I'm following him if I choose to disobey. But...I will still have to be careful.
Four minutes later, Genos is leaving the apartment to follow Saitama.
• • •
City Z is filled with some gang members and old people running their shops. None of them are worried that a monster might appear. Their faces are filled with curiosity.
Saitama is walking next to a father and a son. The son is whining like there's no tomorrow, and the father is trying to shut him up.
Saitama stops and gets into a sprinting position.
Saitama blasts off and sprints around the majority of City Z—looking for monsters but doesn't find any.
Saitama stops near a farm and slaps his forehead.
Saitama (head): What am I doing? I'm never going to find a monster here. Maybe I should go and see what's happening at that old man's dojo. At least that might lessen my severe boredom. Or I could just check the other cities. Either way sounds fine to me.
Saitama turns around because he hears footsteps. He has his serious face.
"Are you a Hero?" Garou says, grinning and panting. He looks beat up. "I'm trying to complete my evolution into a monster. I just got into a short brawl with thirty men not far from here—and won. Nothing too serious. But—you look like a worthy—"
"Stop." Saitama says, putting his hand up. "Let's get this straight...are you a human or—" Saitama starts, but Garou is already up to Saitama's face, ready to punch him.
"Weak punch." Saitama says, punching Garou in the face with ease, knocking him out as well as making him fly into the farm. "If you're not a monster, you're wasting my time." Saitama starts walking away, leaving Garou demolished.
• • •
Ten minutes later, Genos is still on the lookout for Saitama. Genos is in City Z. He scans the area but is unable to find Saitama's location.
Genos (head): Where could Master have gone? My detector says that he isn't in City Z. How can that be? I should've left as soon as he left. I was too precautious.
Genos remembers when Saitama was teaching him the Art of the One Punch. This is a lesson that Genos had high hopes for. He was sitting with Saitama on the top of a business building in City Z.
"All it takes is one punch Genos!" Saitama had said, putting the number one in the air. "Just one." He was smiling with his bored face.
"How should I go about that—Master?" Genos had asked, his voice filled with excitement.
"You must concentrate all your willpower and strength into one full blown attack! Don't back down! Don't give up! Don't flinch in the presence of your enemy! Don't—" Saitama started.
"Master—why don't you show me how it's done?" Genos replied, deep in thought.
"Uhh...no, that's a terrible idea! Actually, it's the worst idea you've ever come up with." Saitama said.
"I see..." Genos replied, looking down. "Then what should I do, Master?"
"Go ahead and try what I've told you on a monster. Remember, focus on your willpower and strength. That's the key. That's your lesson for today." Saitama had replied, scratching his bald head. That is what Genos had done a week later when he was going up against a monster who was potentially a Demon Level threat.
Genos tried what Saitama had taught him—unfortunately, the fight didn't go as Genos had planned: he had lost all his limbs and was on the brink of death. Luckily, Master Saitama stepped in and defeated the monster with just one punch.
While Genos was being repaired as well as getting a new upgrade from Dr. Kuseno, he was furious at Master Saitama.
It was only until Genos was fully repaired that he had lost all anger and frustration at Master Saitama. This was mainly because Genos had other problems to worry about.
Now that Genos realizes that finding Saitama is useless, he turns around and starts heading back to the apartment.
As Genos is walking on the sidewalks of City Z, he gets an emergency call from the Hero Association: MEETING! S-CLASS HEROES ARE CALLED TO THE HERO ASSOCIATION HEADQUARTERS! NOW!
Genos (head): What could the Hero Association need that they must call all the S-Class Heroes? Is it a God Level threat? Or Dragon? If Master Saitama went along, he'd make our mission a 100% success. But—if Master Saitama did join the mission, how would I grow as a Hero? I must become stronger!
Genos starts sprinting in the direction that will lead to City A—where the Hero Association Headquarters resides.
• • •
Saitama checks the rest of City Z—he still can't find any monsters to fight.
Saitama gets into sprinting position and sprints to City F.
When Saitama reaches City F, he first goes to the Public Park, where he had met Speed O' Sound Sonic for the first time not so long ago. His face is filled with agony.
Saitama searches the entire park for monsters but finds none.
Saitama runs out of the Public Park, searches everywhere in City F and still doesn't find any monsters.
Saitama, in the middle of City F, kneels in defeat, grips his head like a psychopath, and goes deep in thought—his eyes bulging.
Saitama (head): This is bad—really bad! Genos wasn't joking! Is this it?! Is this how I'm going to spend the rest of my life?!
"FUUUUUUUUUUU!" Saitama screamed.
A little girl is walking with her mother. The little girl is paying attention to Saitama screaming.
"Mommy, why is that bald man screaming?" The little girl asks.
"It's best to just keep on walking, sweetie..." Her mother replies, forcing her daughter to look away.
• • •
Genos walks down the hallway with Bang that leads to the room where most of the S-Class heroes are—except for Blast, of course.
"Do you have even the slightest idea why they've called us up here, Genos?" Bang asks. He has his hands folded behind his back.
"Not sure. I suspect it has to do with the monster appearance rate." Genos replies, clenching his fist. "It's bothering Master Saitama. I saw it on his face. Maybe I should've never told him."
"Nonsense. You would have only been postponing the inevitable. Anyhow, if that's all this meeting is, son, then they might as well forget about it—don't you think?"
"Not necessarily." Genos says. Before he can say anything else, Atomic Samurai spots them and makes his presence known. He is leaning on the wall—his arms are crossed.
"My my, Bang, if I'd known you took this long, then I would've..." Atomic Samurai started, but was interrupted by Genos.
"Atomic Samurai...Rank Four, do you have any theories about our current situation...the monsters?" Genos asks.
"Huh? Nah. I'm just a little down that I can't get my blade dirty more often because they're nowhere to be seen if that's what you mean." Atomic Samurai replies. "Anyway, we better get going inside and catch up on what we've missed."
• • •
Saitama is now inside a restaurant in City S. Using the money that Genos had given him (Saitama has no idea where Genos even gets that kind of money), he orders some Udon with some Shumai on the side.
Saitama sits on a banquette and stares at the glass table—seeing his own reflection. He is waiting for his meal.
Saitama (head): Some Hero I've become...
Saitama looks left and sees Genos's fangirls sitting on a banquette not far from where he was sitting. They are eating, conversing, and laughing among themselves. All of them are wearing GENOS T-shirts.
Saitama sighs. He looks through the restaurant window and spots something bright in the sky. The ground starts shaking as if an earthquake is about to occur.
Saitama (head): What's that?
Outside, in City S, the pedestrians are smiling with joy as they're walking from street to street. None of them are angry or sad. That all changes with the first glance of one pedestrian.
The pedestrian was an old man. He saw what looked like a beam of light coming in their direction from the sky.
"LOOK UP! SOMETHING'S COMING!" The old man screamed as he felt the ground shaking beneath him.
All the pedestrians looked up and screamed. The beam of light was so bright that it had blinded some of the pedestrians who looked.
Now, all the pedestrians in City S were running for their lives as the ground started shifting and breaking apart.
Saitama is still in the demolished restaurant—looking at the beam of light through the cracked windows. Everyone has left the restaurant in fear that they might be crushed. Saitama is unfazed by all of this.
Saitama (head): Could this finally be my rival? After all those months of boredom—is he really here?
Saitama punches, which creates a big hole that leads him out of the demolished restaurant.
• • •
Most of the S-Class Heroes look terrified—except for Tatsumaki and Watchdog Man.
"Do you understand why I've called you now? Even Shibabawa—if alive, wouldn't be able to predict this event. This means that we're dealing with forces beyond our own comprehension and knowledge." The speaker says.
"Let me get this straight, this entity, is he God?" Zombieman asks. He looks furious.
"Presumably, no. God is a whole other entity by Himself. This mysterious life form can annihilate a galaxy with ease, as I've shown you in the footage. It's also from a dimension called the Void. A dimension created by Bon countless years ago. It's sad that most of you won't live to see it. Even me." The speaker says, grinning.
The ground starts shaking. Tatsumaki and Watchdog Man seem a bit worried now.
"W-what the?!" Superalloy Darkshine says, gripping the table to keep himself in place.
The Child Emperor's eyes are bulging. He clenches his teeth.
"TRAITOR! EVERYONE, GET DOWN!" Child Emperor screams as he jumps out of his chair and summons one of his gadgets to protect him.
A cosmic energy beam strikes the entire Hero Association Headquarters, presumably killing all the S-Class Heroes who were inside.
The impact of the beam was strong enough to annihilate the entire supercontinent—which included all the cities.
From outer space, the earth is being torn apart. In just two seconds, the entire planet explodes—causing planetary brutality.