A/N: Hey guys is Chaos and I'm back with another story. This story is essentially where Asta, Izuku, Yuji and Tanjiro are sent to the universe of RWBY with a goal of stopping Salem and helping defeat the Grimm. This story may have lemons with the ships I have assigned for the 4 boys. There may also be OOC moments so bare that in mind. Now in the case of Asta and Izuku those 2 are going to be powerhouses/Overpowered considering how strong their verses are. I'll also probably give them Aura's and semblance and I'm open to suggestions of what powers I should give the 4 MC's. Also incase your what the timeline I'm using Izuku, Asta, Tanjiro and Yuji its:

Asta - Couple of days after the events of the Movie

Izuku - Sometime after season 5, Izuku can use Float and Smoke screen in this fic

Tanjiro - Around the middle of season 4

Yuji - Couple of days/weeks after season 1

It had been a week since Asta and the gang had fought Conrad and the heroes of the Clover kingdom are still making preparations to raid the Spade kingdom and stop the threat of the Dark Triad. However something unexpected would happen within the Spade kingdom that would change the lives of 4 characters forever.

In the Spade kingdom a man with short white hair, pale skin, wore black sunglasses and had a lab coat with diamond patterns would be inside the room of a spacious laboratory.

The room had several notes plastered on the wall, chemicals on the counter and several medical tools on the counter, with some of those tools having stains of fresh and dried blood on them.

In the middle of the room there was a machine with a long tube at the centre and various wires and cables connected to the machine. In the tube there was a book floating in mid air that was black and red in colour and was giving off a sinister aura.

The cables of the machine were glowing in black energy as the energy was gradually being absorbed by the book as the aura around the book was getting more violent by the second.

'So far the procedure is going quite nicely' The man with glasses thought to himself as he gave out a small smirk. This man was known as Morris Libardirt, the magic scholar of the Diamond Kingdom. He had once taken over the Diamond kingdom by manipulating its king and was responsible for the creation of the new 8 shining generals. However his plans were foiled by Mars and had to flee into the Spade Kingdom. Luckily he had already made contact with the residents of the Spade kingdom and was granted asylum as long as he uses his magic science that is to benefit the spade kingdom.

Despite making a deal with the Dark Triad he had his own ulterior motives where he wanted to study more upon demonic magic and negative mana in order to reach extraordinary heights of magical power and understanding. He had several secret projects to achieve this goal but the most recent one was the experiment he was doing right now.

The light on the machine that was green would suddenly go blinking red as Morris brought out a script that had a strange foreign language written on it.

'Now for the final process to create an artificial grimoire' Morris thought to himself as he cleared his throat and began to speak.

"Nox e caelo cadit. Crescit tenebrae sicut omnis lux moritur. Deprecamur corda vestra et interitum vestrum. Per manum meam nigram, mortui resurgent…"

Morris chanted what was written on script pouring his own mana into a cable that went directly to the floating book. The moment Morris spoke those words the book began to glow brighter in a sinister red as its pages were fluttering from one page to the next. Morris grew more excited as he could feel a connection forming with the artificial grimoire.

The experiment Morris did was to create an artificial Grimoire with the use of negative mana, regular mana he absorbed from 100s of Diamond Kingdom citizens (mostly prisoners) and demonic scriptures he acquired while in service of the Spade Kingdom. This grimoire would not only increase his power exponentially but also give him another magic type, one that would compliment his modification magic.

When Morris stopped pouring mana into the cable the grimoire continued to glow brighter and brighter as the mana within the air was beginning to distort the space around the floating book. It look like the creation of an artificial grimoire was a success, however when Morris was about to walk towards the glowing book the grimoire stopped glowing completely and fell on the floor no longer floating in the air making a noticeable *THUD* sound.

'What?...what is the meaning of this…I completely lost my connection with the grimoire' Morris thought in complete confusion and annoyance 'Not to mention I don't feel any mana being released from the book'.

Morris then pressed a button near the machine as the glass tube would open to still see that the artificial grimoire was on the ground not doing anything. Morris picked it up and began to inspect what could have gone wrong, but there was nothing he noticed with the book that could have resulted in this outcome.

Grunting in frustration and annoying he threw the grimoire aside and was about to leave calling it a day. But just as he was about to make his way to the door, something interesting happened.

The artificial grimoire suddenly swells up releasing an enormous amount of magical power as it glows again way brighter than the previous times.

"Huh?, What the hell is happening?!" Morris yelled in confusion as the grimoire continued to glow, sending violent waves of air throughout the room blowing away various items. The grimoire continued to glow for a good 3 seconds until the book suddenly imploded on itself.

*BOOOM* came the sound when the grimoire disappeared leaving an explosive gust of wind that was so powerful it knocked Morris back, almost making him crash against a wall. Morris slowly got his bearings together as he looked to see that the grimoire was no longer with the laboratory. Morris clicked his tongue in annoyance and muttered something about this being a failed project, unbeknownst to him that his creation would have dire consequences to the world.

In The World of RWBY

Location: Evernight Castle

Salem had just finished having a meeting with her subordinates, especially with Cinder as her task was to acquire as much Dust as possible by any means necessary. She was in her quarters sitting on a chair with her eyes closed. When she wasn't creating grim, killing people or harming any innocents, she would do some meditation as it eased her mind and gather all her thoughts together.

She would have continued to do some more meditation but she suddenly felt something that completely shook her out of her calm state of mind.

'What in the devil, is this?' Salem thought in curiosity as she could feel an enormous amount of magic power coming from outside of her castle. At first she thought it was Ozma but quickly dismissed that idea when she felt how sinister the magic power felt. She highly doubted any of followers could feel the mana radiating outside the castle, so she would have to look into this matter herself.

She opened the large window of her quarters and flew to where the magical power was coming from. After a couple of minutes of flying she finally arrived at the source of that power and what she was looking at seemed to pique her interest.

In front of her was the artificial grimoire floating in front of her glowing in its red sinister aura. Her curiosity increased as she walked towards the grimoire not caring if it were dangerous or not, afterall she was immortal. The moment she grabbed the book she felt an intense surge of power throughout her body. She felt as if she had gotten at least 40 or maybe even 50 times stronger than what she already was. Not only did she feel stronger she could also feel a strong connection forming between her and the grimoire as the pages of the grimoire were fluttering open with words suddenly spewing on some of the first empty pages.

Salem's body then started emitting the same red glow from the grimoire as the power being released from her body felt exhilarating. She looked at the grimoire for a split second until a wicked and sinister smirk spread across her face.

"Well…this is certainly interesting" Salem said out loud

Location:

Outside the Multiverse

Somewhere beyond Space and Time

In a plane of existence that sits outside the multiverse in a realm beyond space and time stood a person. That person floating in the endless void that illuminated the colours blue and purple, that was filled with all sorts of celestial bodies.

The person had pure white skin, white glowing eyes, had an athletic physique and wore nothing but a dark green cloak with a hood, matching green trunks and matching green boots with gloves as well. The being was known as The Spectre A.K.A the vengeance of god.

The Spectre is known as one of the most powerful beings in the infinite multiverse and beyond. His goal is to provide balance within existence and prevent the dark forces from spewing throughout all of existence.

'It is so peculiar…despite there being good, evil will appear. No matter how many times we try to stop it…no matter what we try to do to erase it…evil will still find a way to exit. It's a never ending battle but regardless it's one we must still continue to fight on.' The Spectre thought to himself as he noticed a universe radiating a dark presence.

The Spectre inspected the world and saw it was one where creatures called grim reside and humans reign. Looking more into the world and using his magical ability to see into the future of the universe, he saw that if this being known as Salem were to continue in her goals she would bring the end of her world. Not only that this darkness would spread throughout her universe and eventually several other universes.

Now The Spectre with how powerful he is could have just teleported infront of Salem and completely erase her from existence, but the problem was there is a battle going on between the gods and other gods that could result in the annihilation to all of creation, so that needed his full attention. Not only that but there are rules to how much he could influence realities with his own power. That being said he might not be able to do something, but someone else could.

'Powerful individuals…I say 4 would do…yes that is what I need… those with strong wills and have the heart of a hero' The Spectre mused at the idea. I looked at the first 50 universes and immediately found the 4 individuals that would be perfect for this task.

'Yes…these four would do' The Spectre thought seeing images of the four individuals, One had green hair and was wearing a green costume, another was pretty muscular for his age holding an abnormally large sword. Another one used breathing techniques to enhance his physical abilities and the other had pink spikey hair and had a cursed entity residing in him.

The Spectre teleported out of the dimension he resided and into the plane where the multiverse resides in order to properly teleport his four chosen heroes in one piece. He made a pocket dimension that was completely white in colour to teleport his heroes in so as they don't get overwhelmed when they see the sight of the Specters eyes would then glow and with a wave of his hand 4 lights would appear in the void. The Spectre would hide himself and his presence just as the lights would begin to fade. The 4 lights would reveal to be 4 teenage boys all sporting mixed expressions of shock, confusion, panic and alertness.

"What?! What's going on?! Where the hell am I?!" A teenage boy that had grey ashen blond hair, was pretty muscular, stood at 5 foot 4 inches, was shirtless but wearing black sleeves, black pants and a grimoire tied to his waist would shout in complete surprise from his sudden change in location. This was Asta the Anti-magic mage of the Clover Kingdom.

"What in Kami is this place?!" Another boy would question both in surprise and caution from seeing nothing but a completely white empty void with 3 other people he had never seen before. This boy had black hair with a red tint, a scar on the left side of his forehead, wore black-green chequered pattern haori over a black hakam uniform, with a katana tied to his hip. This boy was known as Tanjiro Kamado, a member of the Demon slayer corps.

"What is going on here?" 'Did those 3 teleport me to this place…no I doubt it they too look just as confused as me. Could this be the work of a villain?' A boy with messy green hair, had freckles on his face and wore a green custom with white gloves, a red belt and red boots would think to himself, staying on guard for anything to happen.

"Uuuuuhhhhh… is this supposed to be training on Domain expansions?" A boy with spiky pink hair, wore a blue uniform that had a red hoodie and red shoes would ask in confusion as he scratched the back of his head. This boy was known as Yuji Itadori, the vessel of Sukiuna. He then looked towards the other 3 boys and immediately perked up.

"Oh hey cosplayers, are you guys heading to a convention or something?" Yuji asked the other 3 boys, earning confused looks from 2 of them but an understanding look from one.

"What? No I'm not a cosplayer, this is actually my hero costume" Izuku clarified to the pink haired teenager though he still had his guard up not knowing what to expect from his sudden change in setting.

"What's a convention?" Asta asked out loud furrowing his brows

"And what do you mean by cosplayer…what exactly is that?" Tanjiro would also ask out of confusion. Izuku and Yuji looked at the 2 sword wielders in confusion considering they didn't know what a convention or cosplay is. Though Izuku speculated that maybe these 2 were probably from rural areas.

"Your hero costume?…that's what you call it?Yuji questioned the green haired teen assuming that his 'Hero Costume' was his own customised Sorcery uniform. "Also If you guys aren't aren't cosplayers then why are you 2 dressed as Tanjiro and Asta?" Yuji casually asked, making the 2 sword wielders turn to him wide eyed as Tanjiro hoovered his hand on his katana while Asta brought his hand to his grimoire.

"Ok what the hell is going on here?! Who are all of you?! And where are we?!" Asta asked the questions that were plaguing the mind of the other three boys. Before any one of the 4 boys could say anything a booming voice and presence would interrupt them.

"The one that is responsible for your arrival…would be me" The Spectre said in a calm fashion. The moment his presence was revealed all boys would turn to him in shock and in fear. They were surprised when a person of white skin dressed in green said he was the one responsible for their arrival but then that emotion was replaced with fear because they could feel the power radiating from this person.

This person was strong, hell the word 'strong' wouldn't do justice from the amount of power this being was releasing. All the boys began sweating and breathing heavily. They had their guard and their weapons up anticipating a fight. They stayed like that for a few seconds until the first person to speak was Izuku.

"W-w-who are you?!" Izuku asked mentally slapping himself that he was stuttering.

"I am the Specter, the wrath of God and mean you all no harm" The Specter said as he gradually reduced his overwhelming presence "I have summoned you here assist in stopping a threat that could bring an end to your worlds and the world of others as well"

"U-um… what k-kind of threat are you talking about exactly?" Tanjiro asked the question that was plaguing their minds in nervousness.

"Before I answer that question, why don't I show what you're all getting into?" The Specter waved his hand, which would lead to the white dimension fading out of existence, as everyone was now standing in a void that was filled with millions of bubbles containing universes in them. The amount of universes they saw in front of them was too many to count, with rows of universes stretching endlessly out in the void.

The moment Asta, Izuku, Tanjiro and Yuji saw this all their jaws dropped, sporting very similar reactions to one another.

"Woaaaaaaaahhhhhhhhh!"

"Oh…My…Lord"

"...M-m-multiverse theory is real?"

"This is soooooooo cool!"

The 4 teenagers continued looking at the beauty of the multiverse for a couple of more seconds until the Specter began to speak.

"As you can all see we a currently standing in the void where all universe reside… and I have summoned you all from each of your different realities to assist me in stopping a threat that is residing in this universe" The Spectres eyes closed as all moved forward and were in front of a universe where they were meant to be sent to.

"In this reality there is a person known as Salem that acquired power due to an anomaly. Because of this she had attained much more power that she planned to use to destroy the world" The Specter didn't go into much detail about the world or their main enemy as there were some things he couldn't reveal. He mainly told them that this world they would be entering is one that has some pretty advanced technology, creatures called grimm and warrior that are referred to as Huntsman/Huntswoman.

"O...K I have to be honest with you this is a lot to process and it is pretty sudden." Izuku said until he looked at the Specter with determination in his eyes "But regardless if its in a different world there are still people that need saving. So I'll gladly go to this universe to help however I can"

"You can count me in on this too" Yuji said, punching his fist against his palm.

"An adventure in another world sounds soooo cool!" Yelled the ashen haired teen

"...Um mister Specter, while I do want to help these people…I still have my responsibilities to protect my sister but also stop the growing threat of Muzan in my world" Tanjiro explained the living manifestation of The wrath of god.

"That will be of no issue Tanjiro Kamado…Time works differently in that reality. 1 minute in your universe equates to 1 year in your reality, and this is something that applies to all of your universe." The Specter explained to the black haired teenager who looked at him in surprise and amazement at such a convenient circumstance. Tanjiro then smiled and agreed to go with Yuji, Asta and Izuku into this new world.

"Hmmm?…Apologies, but we have to hurry now…are you all prepared to enter into this new reality?" The fours boys nodded as they were ready to enter the new world. The Specters' eyes would glow white as all four boys began to glow as they were beginning to teleport inside the world of RWBY.

However Izuku released something a little too late.

"Wait where are we supposed to star-" Izuku didn't have time to get his sentence out as both him, Asta, Tanjiro and Yuji disappeared from the Specters' sight with the Specter also disappearing from the multiversal void.

A/N: And that's a wrap, I was intending this chapter to include some scene of them being in the RWBY verse but I didn't feel like making this chapter any longer. Hope you all enjoyed this chapter and let me know what you think.