"She's here."

She killed everyone I cared about...her hypnotizing golden eyes have deceived me.

She pitted my own friends against me.

His emerald eyes met her golden ones, she showed him a dark twisted smile.

She made a finger gun and said:"Chainsaw."

As if on command an armored creature with chainsaws sticking out of its hands and head. The creature jumped to attack the Omnitrix wielder, but he was quicker and in an green light, he was replaced by ghe humanoid brown dinosaur Humungousaur.

"HUMUNGOUSAR! RAAAAAHHH!" he announced before jumping to attack the chainsaw humanoid head on.

The two warriors prepared to clash.

Everything fades to black as the roaring sound of an chainsaw is heard...

...Ben 10 is dead.


A/N: Hello there and welcome to my newest Fanfiction! This time is a crossover between Ben 10 and Chainsaw Man I call "Ultimate Chainsaw" !

There are a few things you have to know about this story:

1. This story takes place two years after the events of Omniverse, and as thus Ben is 18-years old and has the Master Control and Evolutionary Function.

2. The Devil Hunters, fiends and devils are aware of Ben's escapades and especially his defeat of Dagon.

3. The Omnitrix has reboot transformations in the database.

4. Ben's personality will be a mix between his more mature Ultimate Alien Force version and his more childish Omniverse version.

As always, I don't own Ben 10 or Chainsaw Man, they are owned by Man of Action Cartoon Network and Tatsuki Fujimoto, MAPPA Shonen Jump respectively. I just own this fic.

Warning: This fic is rated M for violence, sexual content, body horror and some stuff involving murder, manipulation and depression.

This fic contains spoilers for the entirety of the Chainsaw Man Part 1. If you haven't read the manga fully or you are an anime-only fan...I'd suggest reading the manga or follow this fic until the anime finishes airing. If you don't care for spoilers and just want to enjoy the fic...go ahead, I don't prohibit you from doing so. You've been warned

Without further wait, plese read this chaoter and enjoy! :)


Present Time.

Ben was at the time in The Plumbers Headquarters, his eyes fixated on the monitor showing an email sent by the Japanese Government for him especially.

"So the japanese government wants me to be part of the Public Safety Sector Devil Hunters of Tokyo? Why? " Ben asked Grandpa Max in confusion.

"They said they'll need someone like you on their team, with you defeating Dagon two years ago." Max answered his grandson as he was copying the paper on a d

"And why should I accept? Devil hunting isn't really part of my expertise." Ben replied as he was fidgeting with his jacket.

"Well, this is your chance to help people, you yourself told me the other day that you are bored with nothing happening in Bellwood. And, you will be able to help people again."

"I guess if it involves saving people I'll go. This hero needs some action again! Goodbye Grandpa Max!" Ben waved as he prepared to leave.

"Ben, don't forget to call me after today! And you sure you don't want some Squid Stew garnished with bugs and shrimps?" Max asked ss whatever was in the boiling pot grabbed Max with an tentacle. Max took out a pan from the drawers and started hitting the tentacle.

"Yeahhhh...no thanks, I'm good." Ben made a disgusted face as he started to walk towards the elevator.

"You sure, Ben? It's fresh!"

"No thank you, Max! I'll be sure to call you tonight!" Ben replied as he took the elevator back outside in the alleyway of "Max's Plumbers" and approached his green and black DX Mark 10 car and drove it towards Mr. Smoothies.

When he arrived at Mr. Smoothies, Ben ordered a strawberry flavored smoothie and a trail of chillo fries. He was eating and chilling when the young hero heard his phone ring. The teenager took it out of his pocked and saw Gwen was the caller.

"Hi nerd. What's the matter? You usually don't call me." Ben replied non-chalantly.

"Hi to you too, dweeb. I called you because I heard you'll be leaving to Japan and I wanted to say goodbye to you." Gwen says.

"Heh, it's not like I'll be gone to Japan forever Gwen, It'll only be temporary."

"I know, but I want you to be careful there with devils and fiends and the like, and if you ever need help or advice, you're always free to call me, Kevin or Rook."

"I will. And I take care of aliens and villains everyday, I am fit enough to defeat some devils." Ben replied with a smirk.

"Allright, bye Ben! Please take care!" Gwen said in an shaky voice.

"Yeah, I'll take care! Bye to you too, cuz." Ben said as he closed the phone and headed towards the airport with his car.


A few hours later, on a train towards Tokyo...

Ben was at the time on the train towards Tokyo, wearing a black T-shirt with his green jacket rested over his shoulder.

Ben's emerald eyes looked out the window, remembering why he was here.

"I hope Max was right about this, I hope I didn't get myself in anything too dangerous with accepting this job..."

The train's intercom was heard, intrerrupting his thoughts.

"Tokyo, Tokyo! Now arriving in Tokyo!"

Ben got up and put his iconic green jacket on and exited to the train station.

Outside, Ben was met with an woman with red hair put in a ponytail and hypnotizing yellow eyes waiting for him next to a silver wreck of a car. Ben assumed she ma

"Hello there. I am Makima, the leader of the squad you'll be assigned to. Please get in the car, your teammates are already inside." the woman said, as Ben guessed, she was indeed Makima.

"Hello to you too." Ben replied as he entered the backdoor of the car.


When he put himself on the back seat, he noticed two other people in the car next to him, a girl and a boy, looking about his age.

The girl had long strawberry blonde hair, red horns coming out of the side of her head, reddish yellow eyes with a cross-target pattern and fangs. She looked somewhat pretty.

The boy on the other hand, looked pretty plain and normal, with scrawny and spiky blonde hair, tired yellowish brown eyes with bags under them with the only unique fe8ature of his being his sharp, fang-like teeth.

"Makimaaa! What took you so looong? And who's this guy?" the boy asked Makima, sounding childish.

"Denji, be quiet and maybe I'll you a treat later, my dog, okay." Makima said to the boy now identified as Denji, making him nod eagerly and make a bark sound.

Ben found this very strange and disturbing at the same time, but he didn't want to think too much about what "my dog" would imply.

"And it took me so long because I was waiting for him to arrive. This is Ben Tennyson, the last member of the sector you are part in. Ben, these are Denji and Power, your colleagues." Makima said pointing to the boy known as Denji and the girl now identified as Power.

"Hey." Denji greeted Ben tiredly.

"Heya!" Power greeted Ben, in a more energetic manner than Denji's.

By that, Ben already found out their personalities. Denji seemed to be tired and childish while Power seemed the type to be energetic and annoying.

After a few quiet moments of being in thr car, it's like Denji and Power went nuts. The two started arguing like children and insulting each other with him calling Power a bitch and her calling Denji a moron.

"Man, and when I thought I'd finally get some peacetul time...!" the teen hero thought as he listened to the two bickering with an annoyed expression.

Power and Denji stopped talking and Ben yelped in surprise as suddenly Makima stops the car in driving.

"Denji, Power. Please be quiet. You aren't little kids, now, are you?" Makima asked the two in a cold voice.

"But he/she is the one who started it!" Power and Denji say at the same time.

"I said be quiet didn't I? Should I remind you that I can get rid of you two and replace you with someone else, it's not like you two are the only devils the organization can get." Makima said coldly, and by the looks of it, she sounded very serious with wanting to kill the two.

Both Denji and Power freeze in fear at the threat, and Ben felt disturbed by the redhead.

"Man, she's really intimidating...yet...I like it?"

Ben was confused, why was he so attracted to Makima, who seems cold and controlling? It was weird, but Ben couldn't help himself but think that way about her.


A random back alley of Tokyo...

Ben, Denji and Power were sent on a mission to kill any devil wandering around the public area, through Ben wasn't comfortable with killing a being, devil or not.

Power groaned in boredom before she hit both Ben and Denji in the head.

"Ow! What was that for!?" Ben asked, rubbing his head in pain.

"I want blood! Can ya get me something I can kill?" Power said making the two teenage boys exhance glares.

"No." both Ben and Denji replied, annoyed by Power's antics.

"Aww...! C'mooon! Pretty please?"

"No. Stop asking Power."

The trio walked through the backstreets of Tokyo for a while, before stumbling into the Sea Cucumber Devil, a creepy giant sea cucumber with a skull and human fingers coming out of it.

Chainsaw blades started appearing out of Denji's head and arms with blood sputtering before finally his head became a chainsaw creature thing.

Ben was surprised for a second, but snapped out of it when the Sea Cucumber Devil attacked him. Without thinking, Ben dialed the Omnitrix and hit the core as an blinding green light surrounded him, making Denji and Power close their eyes, blinded by the light.

When the light died down, in Ben's place now stood a tall humanoid creature made out of rocks and flames, with the Omnitrix symbol now being on his chest.

"HEATBLAST! Oh, yeah, this is gonna get hot!" the creature exclaimed, making itself known as Heatblast.

"Another devil?! What have you done to Ben?!" Denji shouted as he propelled himself towards Heatblast. The alien dodges, making Denji hit his head into an nearby wall, causing the chainsaw blade on his forehead get stuck in it.

"Woah, woah! Stop! Calm down buddy! I'm not a devil, it's me, Ben!" Heatblast said, trying to calm Denji down.

"Huh? But how did you...?"

"Long story. And I could ask you the same thing with those chainsaws coming out od your hands and head."

"Touché. Fine enough by me." Denji replied as he, Heatblast and Power launched an attack towards the Sea Cucumber Devil.

Green blood started pouring out of the creature as Denji cut it with the chainsaw blades.

Heatblast managed to get on top of the creature and blasted

The trio noticed another guy yelling to them that the Sea Cucumber Devil was his target, but his yelling was cut short as the devil rolled off of the building the three were on, falling onto the poor guy and stomping him, killing him instantly.

Denji and Ben remained flabergasted at the event, shocked of the outcome.

"Yay! Blood! Can I eat that guy's blood now that he's dead?" Power asked maked the two give him a glare.

"POWER, NO!" Denji and Ben yelled in annoyment.

"Okay, okay! Geez! You guys are no fun!" Power whined childishly.


Makima's office, following the incident...

"We killed that devil and then accidentally killed that guy! So what?!" Power replied, rolling her eyes at being berated by Makima.

"You three stole the target of a Private Sector Devil Hunter and then prompted to killing him by rolling the Sea Cucumber devil into it. You were all childish, especially you, Power." Makima said coldly with an misleading smile on her face.

"And?"

"And if you don't stop acting like a kid, I'll make sure you'll be cut into pieces, did I make myself clear, Power?"

Makima's response made Power to gulp in fear, freeze and shut up.

"Good. We managed to cover up that incident, but it better won't happen again. You're free to go." Makima said getting up from her seat and leaving the office.

Soon after Makima's exit, the three soon followed suit and left the office.


Outside.

Ben, Denji and Power were at the time walking through an back alley of the street.

"By the way, are you gonna tell us what that whole devil transformation thing?" Denji asked Ben.

"Well..." Ben started. "This is an device known as the Omnitrix. It allows me to store alien DNA and to transform into aliens." Ben replies.

"Oh, cool! So it allows you to transform into aliens? Awesome!" Denji said with child-like enthusiasm.

"Yeah. So what about you Denji? With the chainsaw head and blades?" Ben asked the hybrid.

"Well..." Denji started. "I was a Private Devil Hunter with my devil pet dog Pochita and I was killed on the job. Pochita sacrificed himself and fused with my heart, reviving me into a devil-human hybrid that can cteate chainsaw blades out of my body." Denji explained.

"Okay, okay! We get it! You two have powers and pasts, now enough with those stupid expozition dumps!" Power said a small black cat snuggled up to her legs. "Kitty-kat!" Power said as she lifted the cat in her arms and started petting it and kissing it.

"You really like cats, don't you, Power?" Ben asked the fiend as she gave him a pout.

"I don't like cats, I love cats! They're the only friends I have! I hate humans because of my nature and I also hate devils because the Bat Devil captured my petcat Meowy! But anyways, don't you guys just love cats?!" Power replied energetically.

"Not really, I don't really like cats. What I truly love are smoothies! Especially those from Mr. Smoothies with Peach Nectar and Strawberry flavors!" Ben replied with stars ij his eyes.

"Really!? Instead of loving those fluffy, cute things, you love some filthy drink?!"

"Gasp...! Don't you dare insult smoothies like that! They're the nectar of the gods!"

"You're both wrong! Neither of those are good likings! What I like the most and wish to have is touching a woman's boobs!" Denji said with a perverted smile on his face, making both the teen hero and she-devil look at him questionably.

"Dude, you have issues." Ben said bluntly.

As if thinking of something, Power's face showed a toothy grin before letting the cat go and approaching Denji.

"Denji, will you help me save my cat Meowy? In exhange, I'll let you touch my boobs." Power said with a smirk, showing a bit of cleavage to Denji, causing him to blush.

"T-touch your boobs...! O-okay then, let's go find Meowy!"

"I'm coming too." Ben said, gaining Denji's and Power's attention.

"Ahh, I see, Ben Tennyson seems like a gentleman hero but you are actually a dirty pervert like Denji, haah? Ya want some of my womanly charms, too?" Power said in a flirty voice, making Ben glare at her and blush.

"W-what?! N-No! L-Like hell I'd want your 'womanly charms' as you call them! I'll come because I don't want you two to do anything stupid." Ben said in a flustered yet annoyed voice.

"Okay, then! Let's go!"

The three teenagers started running towards the Bat Devil's hideout where Meowy was being held.


The Bat Devil's Lair.

Ben and Denji managed to infiltrate the Bat Devil's hideout, and were almost close enough to reach the cage containing Meowy but the ground suddenly started shaking as a giant ugly red bat appeared out of the ground, The Bat Devil.

"Sorry guys but...I had to trick you to come here. It was you or Meowy, so...good time getting eaten!" Power said, she sounded guilty but she still had that stupid smirk plastered all over her face.

"What?! You betrayed us?!" both Ben and Denji exclaimed in shock.

"Well, betrayed is a bit too much and-"Power started to say, not noticing the ugly Bat Devil's head coming closer and closer towards Power and Meowy.

"POWER! LOOK OUT BEHIND YOU!"

"Huh? Oh...crap...!" Power said as he body was flung into the air, before falling down the bat's throat, as the creature closed its mouth.

"POWER!!"


And...done! Phew! 3K words for first chapter! This was the first chapter of Ultimate Chainsaw! What did you think of it? Bad? Meh? Okay? Good? Great?

Now, please be polite and respectful in the reviews/comments. Any flames or trolls will be cut by Denji. Only constructive criticism and ideas. Please no comments begging for new chapters or requests. I want the comments to do something for the story!

In the reviews you can vote for who should be Ben's main love interest.

The options for Ben's interests are:

Power

Makima

Kobeni

Reze

Quanxi

An a small sneak peek into the next chapter, Denji, Ben! Take over if you will!

Denji: That Bat Devil gives me and Ben a lotta trouble!

Ben/Rath: Rath will not give up! Rath will crush that bat and break its wings in half!

Denji: We'll save Power no matter what!

Power: Aww... you guys will really save me~?

Waiting for you in the next chapter 'Chainsaw and Omni VS. Bat' !

*Post-editing note: I slightly edited and reworked the chapter, don't worry, I didn't do much to this chapter other than adding a few scenes and deleting some others that dragged the chapter.*

Hope you had good time, please follow and favorite thia story and until next time...see ya! Already writing the next chapter!