A/N: I'd like to thank Rednaut67 for giving me this idea. Just kept buzzing in my head and now I gotta try and write it. This is a monster and hero harem story, so some bits may/will be different. Just saying. Also, this has nothing to do with my other One Punch Man fanfic.

City-A was going through it's usual routine. Men and women going about their jobs. Children at school. Various businesses doing whatever they do.

BOOOOM!

All of which suddenly comes screeching to a halt whenever a monster appears. Just like the one standing up from the massive crater.

Aside from the purple skin, pointed ears, sharp claws on their fingers and toes, and two antenna dangling in front of it's eyes, the monster looked like a woman. After all, men didn't have such large assets like she did.

The monster merely glanced around in disgust before jumping into the sky, where she seemed to float above the city with ease. She spread her arms wide with a guttural roar, orbs of pure energy gathering around her before casting them off towards the city, each strike leaving a massive explosion in it's wake.

"Hmph." the monster scoffed as she gently floated back to the ground, her sharp eyes watching humans fleeing for their lives. "If you humans think you can continuously hurt the earth and not face any consequences, you're wrong."

-Hero Association H.Q.-

The Hero Association was buzzing with movement as people tried to get a correct evaluation on the situation.

"What's the threat level on the monster?!"

"Are there any heroes nearby?!"

"Class-A heroes Smile Man and Lightning Max are on the scene!"

-Smile Man and Lightning Max-

Both heroes, who were held in regard for their Class-A status, were lying unconscious amongst a pile of rubble that used to be a building of some sort, leaving the monster woman to continue her rampage. Other heroes, such as Class-A's Spring Mustachio, Blue Fire, Crescent Eyebroll, Class-B's Double Fall, and Class-C's Mumen Rider, and many other heroes, all valiantly fought with all they had to defeat this creature.

Or as valiantly as they could before all 31 were swatted away like crippled flies, the monster not even noticing any of them.

"Was someone there?" the monster asked while looking around at the area. "Must've been my imagi...nation." she trailed off when she saw a small girl in the distance crying her eyes out.

"Mommy! Daddy!" the little girl cried, oblivious to the monster slowly approaching her. She stared down at the little girl for a moment before raising her hand. It almost looked like she was going to comfort the little girl...had her arm not grown ten times it's size. A sadistic chuckle escaped her throat before she clamped her hand shut. Her grin dropped when she realized that the expected ooze of pulped human girl was not seeping through her fingers. Her gaze shifted slightly to see the girl lying safely on the ground, out cold, beneath another figure being shrouded by a white cape.

"You're a fast one." the monster stated, her arm shrinking back to normal as she addressed the newcomer with mild interest. "Who are you?" She could faintly make out a smirk on the stranger before they turned to face them.

Before her stood a man wearing a yellow jumpsuit, red boots and gloves, and a plain white cape held up by black circular fasteners on in shoulders.

"Just an average guy who's a hero for fun." the man stated, arms crossed over his chest, and a blank look on his face. Also, he was bald.

"That is...the stupidest backstory ever!" the monster guffawed before glaring at him, her whole body facing him. "Well, you told me yours, so I'll tell you mine. I was spawned from the constant pollution brought about by you humans." She then thumped her chest with her hand, her sharp teeth showing as she snarled out. "I AM VACCINE WOMAN! The earth is a single living organism. You humans are nothing but a disease-causing bacteria that eats away at her without end." Her body seemed to shift as she grew in height. "In order to obliterate you humans and your evil civilazation, the earth has given birth to ME! YOU SAY YOU DO THIS FOR FUN?! FOR FUN?!" She now towered over the man as she looked more monstrous than before. She could still be seen as a woman due to the impressive...assets she was sporting with the rest of her new body. "HOW DARE YOU CONFRONT MOTHER EARTH'S APOSTLE FOR SUCH AN INANE REASON! YET, WHAT MORE COULD BE EXPECTED FROM A HU-"

It happened so fast. One moment, Vaccine Woman was ready to strike down the foolish human that stood before her. The next?

BLAM!

Bits and pieces of her now rained from the sky, courtesy of the man's fog-dispersing punch. The man was now looking at his smoking fist, his look of boredom shifting to a mixture of anguish and frustration.

"Again?" he muttered to himself before falling to his knees. "Another monster beaten with just one punch?!" He gripped his hands and threw his head back-

"uuugghh..."

But was stopped short of screaming his frustrations to the heavens by the sound of groaning coming from a particularly large piece of blood soaked piece of what remained of Vaccine Woman.

"Owww." came a tiny voice as the meat fell apart, a tiny figure fumbling out of it. "Sweet Mother Earth! That stung!"

"Uh...are you that monster's baby or something?" the man asked as he stood over the creature. It looked like a smaller, cuter verson of Vaccine Woman.

"Huh?" the monster girl blinked before realizing who it was. "GAH!" she yelped before jumping back. "You rotten hu-whoa!" she cried out when she began slipping on a pool of blood, her arms flailing wildly in an attempt to keep her balance before ultimately falling face first.

"Are you okay?" the baldy asked as the little girl sat up with a groan.

"Why do I feel so...weak?" she asked herself before looking down at her body. Her tiny body. "AHHHH!" she shrieked in horror as she began dancing around and looking at each part of herself. "WHAT HAPPENED TO ME?!"

"Well, you're small and naked." he stated, earning a growl from the girl.

"I know that! I wanna know why!"

"Well, are all creatures naked when they're born?" he asked.

"NOT THAT, YOU DIPSHIT! I WANNA KNOW WHY I'M NO BIGGER THAN THAT LITTLE GIRL OVER THERE!" she wailed while shaking her fist at him.

"Huh?" he blinked before the dots connected. "Wait. Are you that monster I just punched?"

"YES!" she snapped before grumbling and looking at her tiny form. "Or at least what survived."

"Oh. Okay." he said before raising his fist.

"AH! NO WAIT!" Vaccine...Girl? shrieked out, waving her arms about. "I GIVE UP! I GIVE UP! DON'T HIT ME AGAIN!"

"Really?" Saitama asked curiously, his fist lowered and his stance relaxed. "Most of the monsters I meet don't usually give up just like that."

"Look at me! I'm small! My power's are gone! I probably couldn't even stand up to a regular human!" she said in annoyance while glaring daggers at the man. "And it's all your fault!"

"How is it my fault? You were trying to destroy humanity. I stopped you." Saitama explained like it was a common thing. Which, considering how monsters and heroes are, was a common thing.

"I was acting on behalf of Mother Earth! She wanted the evil, pollution inducing humans dead!" she yelled while stamping her foot.

"There are better ways to fight pollution besides destroying humanity." he said, causing the girl's antenna to twitch.

"Rrrrgh!" Vaccine Girl growled before turning and stomping away. "You know what? Fine! I'll give up on destroying humanity! But I'll be back to kick your ass, you bald asshole!"

'You're bald too.' he thought in annoyance before he too left the scene, right when a man with three scars over his left eye a fair distance away was being praised for destroying the monster.

A/N: End of part 1. More will happen. I just want some opinions from all of you.