A/N: A little one-shot for fans of One-Punch Man, Ninja Slayer, or both.

Note that bold in quotes means "energetic yells"

And regular bold is the narrator.

It was a sunny day in City Z. Citizens milled about, shopping, eating, and so forth. In fact, one particular citizen of City Z was walking in the streets. He was the bald hero known as Saitama.

However, Saitama wasn't alone. There was a certain ninja watching him, studying his movements. This ninja was on a building's roof, staring at his enemy through binoculars.

This is yet another opportunity to test my new weapons. Sonic thought. Let the battle begin!

Suddenly, a ferocious yell echoed throughout the city:

"YYYEEEEAAAAARRRRRTTTT!"

A crimson being smashed into Sonic, sending him flying off the building and into the ground, in an alley. He rolled a few times, and then got up slowly. He re-focused his eyes, and then got a better look at his attacker.

The attacker was a man in a crimson ninja uniform, complete with a ridiculously long scarf. His face mask had engravings on it, and there seemed to be a green aura around him.

"You… Who the hell do you think you are?!" he growled.

A deep voice greeted him. "Domo, Speed o' Sound Sonic. I am Ninja Slayer!" The red ninja said, bowing. An explosion appeared behind him.

Sonic was a bit irritated by the politeness, but he was a ninja; he knew his manners.

"Domo, Ninja Slayer. I am indeed Speed o' Sound Sonic. Why did you attack me?"

Ninja Slayer didn't hesitate to reply. "You are an evil ninja, are you not? My mission is to eradicate ALL evil ninja."

"Your mission, eh? Well then, Ninja Slayer. Prepare to die at the hands of a ninja!" Sonic said, drawing his sword.

Ninja Slayer got into a fighting stance. "Prepare to recite your death haiku!" he said.

He charged at his opponent. "Yeeart!" he yelled, thrusting his hand out.

Sonic smirked, and then vanished in front of Ninja Slayer.

Oh my Buddha! Sonic seems to be quite the speedster! How will Ninja Slayer counter this?

Sonic appeared behind the crimson warrior and brought his sword down. "Die, Ninja Slayer!" he yelled.

However, Ninja Slayer's power was far from ordinary. He turned and grabbed the sword with his hand.

"What-?!" Sonic began. He was cut off as a crimson fist slammed into his gut, knocking the wind out of him.

"Yeeart!" Ninja Slayer yelled, thrusting his fist forward, and sending Sonic into a dumpster.

Sonic groaned. How strong is this guy? He wondered. I shouldn't be going easy on him!

Ninja Slayer walked over to the dumpster. He broke Sonic's sword with his hands. "Have you recited your death haiku?" He looked inside the dumpster, but saw no sign of the enemy ninja.

"Where did you go-"

"WIND BLADE KICK!"

A foot smashed into Ninja Slayer's skull, sending him into the ground with a WHUMP.

Sonic, bruised, leaped onto the ground with a flourish.

"You fool. You shouldn't have underestimated my speed."

That was disgraceful! You shouldn't have let your guard down! Naraku Ninja said in NinjaSlayer's mind.

The dark-red ninja ignored the voice and got up.

"Playtime's over, ninja. I will bury you." He growled.

Sonic smirked. "I was thinking the same thing."

Ninja Slayer jumped into the air and threw several dozen suriken. These weapons are different than regular shuriken; they are powered by supernatural stuff, meaning our hero never runs out of ammo.

Sonic, seeing the incoming projectiles, decided to fight fire with fire. He threw several dozen of his own shuriken at the opposing ninja.

Would you look at that! The wave of suriken and shuriken have made visibility poor! Who will be left after it's all said and done?

After what seemed like 10 minutes, the waves of sharp, small projectiles died down, and lo and behold, our two fighters were still standing.

Sonic had a few cuts where the suriken had cut him. Ninja Slayer, however, had no visible cuts.

"Impressive. You are still standing. But this is where your life ends." Ninja Slayer said. He got into a stance, and then dashed forward towards his enemy.

"FOUR SHADOWS BURIAL!" Sonic yelled. He began to move, and four identical afterimages appeared.

Oh my Buddha! There's now 5 Sonics! Which one is the real one?!

Ninja Slayer, undeterred, hurled his fist at the nearest one. The afterimage vanished, and Ninja Slayer turned around.

"Scattered Flash Slash!"

The three afterimages and Sonic attacked Ninja Slayer at the same time.

Holy moly! They've all attacked Ninja Slayer with their ninjato!

"YYEEEAAARRRTTT!"

The three afterimages disappeared and Sonic was thrown back.

Our hero is still alive! What a show of strength!

Ninja Slayer was alive. Blood was oozing from some cuts, but otherwise, he was still alive.

Ninja Slayer dashed to his enemy and delivered an uppercut to Sonic's jaw.

"YEEART!" he yelled as the punch smashed Sonic up into the sky.

As Sonic flew into the air, Ninja Slayer jumped up, delivering rapid fast chops and punches.

"Yeeart!"

"Augh!"

"Yeeart!"

"Augh!"

"Yeeart!"

"Augh!"

Finally, after what seemed like forever (it was really 5 minutes) our hero delivered an axe kick to Sonic's head, sending him back to the ground.

Sonic was badly bruised, and knew that he was beaten.

He slipped out some pellets and hoped that he had enough strength left to run.

Ninja Slayer landed on the ground.

"Prepare to die." He said.

"Not today, Ninja Slayer!" Sonic replied. He took out the smoke pellets and threw them at the ground. Immediately, they exploded, and a white cloud of dust engulfed both ninjas.

Oh my Buddha! Sonic has used smoke pellets! But will they even affect Ninja Slayer?

"You fool. I am a ninja as well. Smoke pellets are useless."

Ninja Slayer ran out from the cloud, but Sonic had vanished.

Where- our hero thought. He looked up, and saw a little patch of purple. The purple on Sonic's scarf, that is.

With a tremendous leap, Ninja Slayer landed on the apartment building. Sonic was limping, his strength was nearly gone, and he was bleeding profusely.

"Don't kill me!... Aren't you a hero?" Sonic croaked, as he collapsed to the ground.

"All ninja must perish." Was his reply.

Yes, yes! Now, smash his head with your foot! Crush him! Destroy him!- Naruku Ninja said.

"Oh, hey, Sonic."

Both ninjas turned and saw that there was a bald man sitting on the roof, eating salmon sushi.

"You!-" Sonic gasped.

Ninja Slayer turned and bowed. "Domo. I am Ninja Slayer. Who are you?"

The bald man smiled. "My name's Saitama. I'm a hero for fu-wait; I'm a professional hero."

"I see. Do you know this evil ninja, Saitama-san?"

"Yeah, I do."

Sonic was getting irritated by the minute. "Are you going to kill me or what?!" he shouted to Ninja Slayer.

"Wait… you were gonna kill him?" Saitama said to Ninja Slayer.

"Yes."

"Why?"

"He is an evil ninja. I must kill all evil ninja."

"Well, I can't let you kill this one." Saitama said.

"Are you saying that you shall challenge me?" Ninja Slayer said, getting into a fighting stance.

"I guess I am. Let's see what you're made of." Saitama replied.

Ninja Slayer dashed towards the bald hero, arm stretched back. "YEEART!" he yelled.

Saitama stayed silent as he dashed towards his new enemy, his arm stretched back as well.

The two punches collided, and there was a brilliant flash of white.\

Who won the battle? Find out next time!

A/N: Chapter 5 of my other fanfiction, Heroes and the Grand Magic Games, is 75% complete.