Hello. You may recognize me from my other story, Martial Warrior. If you read that complicated crossover, 1. Thank you. 2. Do not worry. This story will not delay chapters there.

Since I no longer write MW at work, I'm left with much free time. So to solve this, I will write this fanfiction to compensate for the extra time.

OPM Webcomic/Manga and Demon Slayer Manga spoilers.

I hope you enjoy the first chapter of Flashy Slash!

Chapter 1: To Aid the Timeline

Flashy Flash was facing a crisis.

It was not terrorists or ninjas. He could handle those.

Not monsters or science experiments. He killed them on the regular.

No. It was far worse.

A mental crisis.

The S-Class Rank 13 hero was currently laid back in a bathtub. His eyes stared upwards at the wooden ceiling. Steam filled the room and covered the mirror.

Flash tilted his head to glance at the sword on a nearby chair. The weapon known as The Legendary Demon Blade seemed to mock him with its glow.

The weapon's original owner, the former ninja village leader, had been defeated. Not by Flashy Flash or his "rival" Speed-o-Sound Sonic. But by an inexperienced bald guy with no sense of technique.

Sonic and Flash received a demon sword after the leader's defeat, as well as some ancient scrolls that had been left behind that revealed otherworldly techniques. Said scrolls remained locked away in a safe not twenty feet away.

They are also the reason why Flash was struggling.

The hero never boasted about his speed. It was not his style. But that didn't mean he didn't take pride in his abilities. The speed he possessed meant everything to him. The mindset of knowing you were the fastest one in the room calmed him to no end.

Then came that fateful day when he had encountered not one but four individuals who were faster than him. His sword, Insta-kill, also broke due to an accident which was just icing on the damn cake.

Flashy had continued to train to catch up to them, but more and more people had arrived on either his level or above.

It was apparent how much stronger the ninja village leader was when the techniques in the scrolls were next to impossible for Flash to replicate. Even the one he did manage to learn was rough, to say the least.

The ninja grit his teeth before punching the sword off the chair. It clattered across the ground but remained unharmed.

"The fuck is the point!" Flash stood up. "I'm not the fastest anymore!"

He stepped out of the bath and began drying himself with a towel. Once finished, the hero put on his hero costume and left the bathroom. Perhaps training would take his mind off things.

His uniform was a tight black bodysuit with white light armor partially covering his upper torso.. A sheath hung on his left side which he slid his sword into.

The hero turned to look at the safe which held the scrolls. He scoffed before twisting around to head towards his door. Grabbing an apple from a fruit basket on the way.

Flash exited his room and looked down the hall to see someone had left the elevator. The doors started to close, but in an instant the hero had appeared inside. A loud crunch echoes as he bites into his apple.

Unfortunately, someone heard this and realized someone was inside. "Hold the elevator!" called a high-pitched voice.

God dammit. Why didn't he just take the fucking stairs? It would have been faster.

Regardless, he laid the back of his knuckle against the side of the elevator door. He heard the individual running towards him.

Judging from the sound, the person was light and short. So likely a child. The voice sounded high pitched which reinforced that statement. It also sounds female, and the noise of her running also indicates high-end shoes.

Which led to it being one person. Considering one of his neighbors on this floor was none other than the new A-Class hero Hellish Blizzard.

A teenage girl turned the corner. She had black hair with a light blue highlight covering her face. A lily rested on the left side of her head.

Lily of the Three Section Staff wore a suit that fit with the motto of the Blizzard group. In her hands, she held, well, a three-section staff.

When Lily noticed Flash, her eyes shrank so small that they were barely noticeable. Her body became pale as fear grabbed hold of her.

"Mr. Flashy Flash, sir. I apologize for intruding." She stumbled into the elevator. Her voice became quieter as she spoke.

"Don't worry about it." The S-Class responded. Maybe he could still take the stairs? Nope. Doors just closed. This was a ten-minute ride. Fuck.

He hated the hero association's new base of operations. It was convenient, but he still had to encounter rich people on the regular who asked him to do jobs for them. If anything, this shy girl was at least manageable.

Speaking of, this girl was shaking like a machine.

"Stop shaking."

"Sorry."

"Stop apologizing for being scared."

The two of them stood in silence for a couple minutes. Lily shifted her hair to hide something under the right side of her face.

Flash decided to break the silence. "Take no offense, but what brings a Class B to HQ?"

Lily seemed to relax a little. "Miss Blizzard told the rest of the group to get stronger to keep up with her. I come to visit her often though and train at the Association's B section. Of course, no other B-Classes like training here so it's just me."

"Good to see someone amongst you take training seriously." Flash decided to offer some rare advice. "Don't let all the super powered people get you down. I've met people with no natural born abilities surpass even the greats with natural powers."

The girl perked up at the news and color slightly returned to her face.

Flash remembered a certain bald hero. "Even the Tornado of Terror."

Lily heavily cringed at the mention of the Number 2 S-Class hero. All new colors returned to white as fear took over.

"You keep hiding the right side of your face. More so than usual. Tornado have anything to do with that."

The B-Class swallowed before slightly moving her hair to reveal a vertical large cut had barely missed her eye. Stitches could be seen keeping the wound together. It seemed new from how red it was.

"I accidentally came across Tornado in the hallway one day. She started picking on my weakness any chance she got. Finally, yesterday, I snapped and yelled back." Tears started to flow down her face.

This probably wasn't her only wound. Flash heard a hero had been slammed through three walls a week ago by the Number 2 hero. Three, being that it came from not one attack, but said hero had been dragged across each room until everything had been destroyed in each one.

Lily probably didn't visit Fubuki just to see her, but rather to allow the A-Class hero to use her psychic powers to heal the child.

Flash kept his poker face, but deep down he was pissed. It reminded him of how the ninja village would punish anybody for being an inferior fighter.

"What is it you said to the Terrible?"

The girl sniffed. "Leave me alone. That is all I said. I told her to leave me alone."

The door to the elevator opened, and Lily rushed out. Wiping away tears as she ran to the training room.

Flash exited and began to reach out to the girl. He stopped when she ran into a room. His hand slowly returned to his side.

"I know how you feel, Lily. To have your greatest pride shattered in not just an instant, but consecutive moments that end up breaking you."

Flash looked down at the hilt of his sword. Guess it was time to train.

He entered the S-Class training area. The best way to describe it would be huge.

The room could fit a whole city block. Metal Knight made no shortcuts for allowing the world's strongest heroes a proper way to train.

In the far left corner, a gym had been set up to allow the heavy lifters to do their bodybuilding. On the opposite side, a kitchen had been set up. Possible for Pig God.

On the right side, next to the door, stood several high-density training dummies. Most likely for weapon users like Atomic Samurai.

In the last corner was a workshop. For machine users like Child Emperor. When he still worked for the HA.

And for what he came here for, in the middle was a hole that had an angled track along the sides. This was placed for Flashy Flash in particular.

Flash walked up to the edge of the track and flung the remains of his apple in the trash. He then started performing basic stretches to prepare for his run.

Today was Friday, speed test day. Whenever he conducted them, a fifth of a second decrease was always his goal. Flash had been successful in this goal for ten years. However, recent events encouraged him to increase that time by a tenth.

This would be his second week attempting the change.

The ninja heard the door open. He turned to see that Tank Top Master had entered the room with a towel on his left shoulder. A commotion could be heard outside, so Flash assumed Master had brought his Tank Top Army with him.

"Flashy Flash," The large hero greeted. "Another day of training?"

"Is it not obvious?" He grumbled. Flash had nothing against Tank Top Master, but when it came to talking to other S-Class heroes, he just tried to avoid it.

"Well, good luck. We powerless people need to stick together to beat those machines and psychics." Master responded. The man clearly knew to keep his distance from Flash on days like today.

They went their separate ways with the ninja leaning forward onto his hands. "Begin countdown!"

The AI programmed near the track detected the hero's voice. "Proceeding. Beginning in 3…2…1…"

When the alarm sounded Flashy Flash disappeared, and soon the whole track became white as the hero raced his previous record.

Tank Top Master whistled from his squatting position. The ninja never failed to impress him. Stubborn or not.

Flash had to complete ten thousand laps in a certain amount of time. Of course for him it wouldn't take nearly as long as some would think.

Unlike other days, the S-Class hero's mind began to wander.

There were six people who Flashy Flash knew were faster than him.

Platinum Sperm. Although dead, the monster's abilities remained locked in the hero's memories. His triple threat match with Garou led to Platinum Sperm utterly humiliating Flash by calling him a fake hero.

Garou. Although this man was still alive, it was unlikely his speed would match Flashy Flash's any time soon. But the memory of how Garou treated him as an afterthought infuriated him to no end.

Blast. This one didn't bother Flash as much as the others. He was the number 1 hero for a reason so he would be the last guy to worry about. Blast's victory over the ninja leader also made his wounded pride against him even smaller.

Saitama. How in the hell did that guy get so fast out of nowhere. Even if the man had no superpowers, having it take three years to surpass fucking EVERYBODY was bullshit. Not even up for debate.

Then King. Damn him. He was never one to boast his speed. But it was still annoying.

Then came the one that pissed him off the most. The Ninja Village Leader.

Flash didn't even know if this man was alive. He got slammed by Saitama in their last encounter. Nobody even second thought on whether he was alive until later.

–

(2 weeks before)

Flash laid down in his bed. After such a long day of killing old members of his former ninja village, the hero could finally rest.

A quiet voice then began to speak to him. He couldn't hear it at first before it finally became apparent.

"Did you remember to check the body of the Leader?"

Silence filled the room. Then the ninja sat up in bed at light speed.

"MOTHER FUUUUUUUU…!"

–

Still beating himself up on that one. Also probably his neighbors.

The sword almost seemed to intimidate him in its sheath. Flash grit his teeth as he began putting more effort into running.

The scrolls were filled with knowledge that the hero couldn't even comprehend. Rumors were that the Ninja Leader could perform those techniques with next to no difficulty.

Yet the only one he managed to get down was an enhanced version of his own original move. The Flashy Slash.

Master heard a yell of anger from the center track. Flash's speed increased even more. The white blur ceased to be for a second before the shockwaves struck the walls.

"I've never seen him move this fast before." Tank Top Master swallowed. "He's pissed about something."

In flash's perspective, the track was barely noticeable. Heat surrounded his body as the speed he was moving began to ignite the atmosphere.

"I need to get faster! Faster! FASTER!"

Flashy Flash's cape flew off him as it couldn't take the speed. The ground began to crack from the force his legs were putting on it.

Then with a final roar, the S-Class Rank 13 hero put everything he had into his speed. And everything became silent for a few seconds.

Until the buzzer went off.

Flash stumbled to a stop. Falling onto his hands. Breathing heavily. Steam rose off his uniform.

"Flash!" Tank Top Master ran over. The ninja held up a hand to signal he was fine.

"That had to be a record." The hero panted. "It just had to be."

The computer calculated the results. "Time till completion increased by .5 seconds."

The room was quiet. Neither of the S-Class heroes could speak.

What.

He had gone slower.

The machine had to be broken.

No.

"I've hit my limit. Haven't I?"

Tank Top Master said nothing. It answered everything.

Every human being has a limit. Various people spend their whole lives trying to break it with only a few being successful. Even then, there was always another.

Flashy Flash had broken his limits a long time ago. It was why he had managed to become so fast. But now, it appears he has found the next wall.

And the hero was no longer confident that he could push through.

The door swung open. The two heroes looked over and saw Tank Top Girl panting in the doorway.

"Master, can you break up some fighting?"

"I would be happy to, but why does it concern me?" Tank Top Master responded.

"Because the Tank Top Army and the Blizzard group are going at it."

The larger S-Class growled. Flash retrieved his cape. "Do you mind if I tag along?"

"No, I may even ask for a favor." The two heroes made their way to the door. Tank Top Girl then led them down the hall.

They walked past the A-Class training room so it wasn't them. The C-Class Tank Toppers would always train with their upper teammates so that left…

The three of them came to the B-Class room. TT Girl opened the door for the two of them. Once they were inside, they took in the scene.

It disgusted them both.

Many Tank Toppers surrounded a single position in the center of the room. There, Tank Top Black Hole had his foot placed on the side of another hero's head. Said hero was unmoving.

The Blizzard bunch was also fighting in the back. Fubuki was screaming at the tank tops and reaching an arm for the center.

"This is a win for the Tank Tops boys! Especially if this is the best the Bitch Bunch has!" Black Hole yelled with his fist in the air.

Other B-Class heroes could be seen trying to pull the army away from the group. But there were only a handful low class heroes to do so.

Until now of course.

"TANK TOPS, TO THE WALL! NOW!" The voice of Master had such force that the walls shook. Even Flashy Flash flinched.

It took not five seconds for the army to run to the wall. Fear spattered their faces. Tank Top Girl did the same as them, but her focus was on the hero in the middle.

The remaining B-Class heroes along with the blizzard bunch and a few extras, either stood back in fear. There was a few exceptions like a guy in a green tracksuit and glasses running up to the injured hero. Blood could be seen on their suit. Besides them was…

Suit.

A broken three section staff.

And a bloody lily on the ground.

Lily.

Flash appeared next to the Girl and the B-Class in an instant. He pressed his fingers to her neck.

Thu-Thump…Thu-Thump…Thu…Thump

"She is alive, but needs medical attention!"

"Lily! Blizzard knelt next to the girl.

Master turned to TT Girl. "Contact the building's paramedics."

"Yes, Sir!" She sprinted to an emergency phone on the wall, and began speaking into it.

Flash shifted his body so that his cape shielded Lily from the eyes of the Tank Toppers.

Master saw this. "Face the wall!" All the Tank Tops did as they were told. The fuming man walked over to the improvised medical team. " Her injuries?"

"Reopened. She was the hero Tornado threw through a wall." Flash responded.

"Tch," Tank Top Master gritted his teeth. TT Girl finished the call and ran up to kneel by Lily's side.

"They'll be here in fifteen minutes."

"Gla…Glasses?" Lily spoke slightly. Her voice was much lower than before. The tracksuit hero nodded. He brought a weak smile to the girl's face. "It's so good to see you again."

"Don't mind him Lily. Are you okay?"

He signed. It would be for the best that they take these injuries seriously.

Flash stood up and went beside Tank Top Master. "Do we know what happened?"

The S-Class Tank Top turned to the non-Tank Top heroes. "Who knows the story?"

The hero known as Needle Star took a step forward. "The Tank Toppers and the Blizzard group they declined and started mocking the Blizzard group."

Lily tilted her head to the speaking hero. "Needle Star, too? Everyone is here. It's good to see you too."

Needle Star went and knelt next to Lily as Tank Top Girl continued the story. "Blizzard group and the Tank Toppers weren't having it. Black Hole then challenged her to a fight and launched an attack before an answer was given."

Tank Top Girl continued to inspect Lily for more injuries. "When she easily dodged Black Hole and smacked him in the eye, the others joined in. That's when I went to get you."

"Black Hole, step forward!" yelled Master. A hero in a black tank top turned around and did as instructed.

Master walked until he was in front of Black Hole. Said man had a swollen right eye which went with the story.

Actually, many Tank Tops had scuff marks on them. Lily must have put up one hell of a fight.

"Flash," Master called out. "Can I make a request?

The ninja walked up to the bodybuilder as the man began whispering into his ear. Normally, Flashy Flash would ignore Master. But this would become too interesting to not participate.

After a few moments, Flash stepped forward.

"Black Hole, I want you to punch Flashy Flash."

BH looked confused. "Won't he just attack me back?"

"He will. But what he will not do is move his legs."

The hero looked between his master and the ninja before getting in a fighting stance. If Flash wasn't going to move his legs then it shouldn't be a problem.

"Hyaah!" A right hook slammed into Flash's jaw. His head recoiled back, but his feet never moved.

"How's that?!" The B-Class yelled after taking a few steps back. It felt great to hit an S-Class with no repercussions.

Flash was still for a second before his eyes returned to BH. "Is that it? No wonder you needed help to defeat Lily."

"Huh?"

"You ready, Flash?" asked Master.

"Like I need to be."

Master looked down the wall. "You all chose to fight a battle you knew you could win. For you to be heroes, sometimes you need to fight someone stronger. Even when victory is not guaranteed. Now, all of you will fight Flashy Flash without him moving."

"HUH?!"

–

Lily sat in a hospital bed for the second time that week.

There was no window to look through with hero headquarters being a large bunker. This left her eyes to wonder elsewhere, like her hands.

Three of her fingers had been broken. Both pinkies and the right index. Bandages covered her hip which had three fractured ribs. Her right ankle was broken with her left arm being dislocated. All of this, plus the dozens of reopened cuts on her body.

Her injuries would put a wedge in her training until they healed, even with Metal Knights technology.

If she would continue.

She already told Fubuki about her thoughts on leaving the hero industry. This thought had come up after the Tatsumaki incident. Her mentor had encouraged her to keep going.

Not this time.

Fubuki said she'd support any decision she made. Whether it be leave or stay. If Lily did leave then she would still be able to hang out with the group.

But if she left, that meant going back to live with her father. Someone who barely spoke to her anyway. His drinking prevented any changes to that relationship. It was the whole reason she became a hero to begin with.

The Blizzard group was the closest she had to an actual family. But with everything that has happened recently, how can she stand beside them?

There was a knock on the door. Lily quickly straightened her hair before calling to them to come in.

A massive man slid sideways through the door frame, before standing straight. The patient nearly had a heart attack when she saw his face.

"Tank Top Master! What are you doi….Pfft!"

Lily covered her mouth to stop herself from laughing. Her fear of the S-Class hero now gone.

The bulky hero wore a newly tailored suit that was black all over. It came with pretty much anything you would wear at a wedding. All except the tank top that had been put on OVER the jacket.

"Yes, I get it. The tank top is supposed to go under the suit. There is one underneath as well." Master had clearly had this conversation already.

Unannounced to Lily, it had been with the same man now eavesdropping from outside the door. Flashy Flash. Who had outright stated that Master looked extremely silly.

Flash listened to the conversation outside. He had no intention of having any more social activity with anyone else today. Not even Lily. Thou, he would show up to make certain she was okay.

Master stiffened up before bowing at a 90° angle. "On behalf of the Tank Top Army, I apologize for the inappropriate behavior shown today. Those who participated are being punished as we speak."

Lily waved her hands in the air. "You don't have to bow! You are a Class S. I should be the one bowing to you."

"Not all of us in S-Class are hot-headed. For example, Pig God, Zombieman, Silver Fang, Puri Puri, Metal Ba…okay, Metal Bat is hot-headed, but he won't wallop other people for no crazy reason."

The Blizzard member sighed. "Sorry, it's just been a complicated week."

The two went into silence. Master fully understood what had happened to Lily earlier this week. But even if he was there, what would he be able to do? Tatsumaki far outclassed him in every way. If almost any other hero had been there, she would have crushed them too. Even most of the of the S-Class.

Well, with a few exceptions.

"Flashy Flash also sends his best wishes." said Master. Outside, Flash's attention becomes firm.

The girl didn't seem that affected by the news. She nodded and continued to look out into space.

"Did you know that Flash was born with no powers?" the S-Class continued.

"Yes."

"Did you know that he would be my fifth pick for hero to go up against Tatsumaki?"

THIS caught Lily's attention. "Why?"

Master grabbed a chair and wiggled his massive frame into it. "First is obviously Blast. From what I know, he is a freak of nature.

"Second would be Metal Knight because god knows what that man has hidden.

"Third would be Silver Fang because he might be able to talk her down, if he was still a hero who could be called upon. Unfortunately he is retired. Fourth would be King.

"And for Flash…"

The hero leaned back and looked at the ceiling. "I watched him defeat a Dragon Level Threat with a single move. Rumor has it that he also defeated two dragon threats at once during the MA battle. With the cherry on top being him going toe-to-toe with both Garou, and the most powerful monsters we have ever seen, Platinum Sperm."

"But how could he defeat Tornado?" Lily asked.

Tank Top Master looked at the girl with a smile on his face. "Flash is very realistic. When Metal Bat tried challenging Tatsumaki to a fight, he stopped the confrontation because he knew Bat would lose horribly. But when Tornado insulted him, he had the guts to yell back at her. And you know what she did?"

He put a hand over the side of his mouth to make certain nobody else heard. Lily leaned forward to listen. "Nothing. She is 100% confident in her ability to defeat him."

The girl swallowed. It was a lot to take in. That someone could stand up to Tornado in such a way.

Master slapped his hands on his legs. "Remember that, Miss Lily. Every person has a chance to become extremely powerful. Even us powerless ones."

Lily's mood had brightened. Not by much. But enough to help.

Flash heard enough. He began walking away from the door, towards the elevator. The ninja did enough for today.

The destruction of the Tank Top Army took less then sixty seconds. Though he couldn't move his feet, the S-Class hero was still incredibly strong. Taking a punch from Platinum Sperm proved that. The Tank Tops stood no chance.

His strength was on par with most A-Class heroes. Add his reflexes and there wasn't much the meatheads could do.

The army was now going through an ITE(Intense Training Exercise) led by Tank Top Girl. With them already being exhausted, the workout was destroying their mental state.

Flashy Flash was about to take a step into the elevator before he disappeared, running up the nearby stairs faster then the eye could see. No way in hell was he risking another ten minute elevator ride.

The hero did not know what to think about Master's words himself. Especially after what had just happened in the training room.

He was getting slower.

Thou, it probably didn't help that his mind was so clouded by doubts. Those did tend to decrease performance. But it didn't make sense. He felt himself go faster. Why did his time decrease by twenty seconds? For someone of his speed, that was life or death.

He went up to his door, and pulled out his keys. Moving past this obstacle would start tomorrow.

Breaking his limits would be no easy task. Better increase his training regiment and, unfortunately, lighten up on the luxuries.

He hated having to do that.

The ninja threw open his door. No missions had been given to him today. Which was odd but that would explain why only Tank Top Master was the only S-Class who he saw today. The others must have been on missions.

Opening his fridge, he grabbed a water bottle and drank from it. Once finished, he tossed it towards the recycling can. Then turned to head to the bathroom.

Then froze.

Where was the sound of the bottle landing.

An odd thing to notice but when you have trained like he has your situational awareness tends to peak. Plus, he would have heard the bottle had it landed literally anywhere with his hearing.

Flash unsheathed his blade and whipped around.

His eyes widened what was once his own apartment inside the largest bunker in the world had been transformed into an open field outside, under a clear blue sky.

Knee high green grass flowed in a calm wind beneath him. No wildlife could be seen for hundreds of meters.

"Where am I? Am I dead?"

It must have been the only explanation. An assassin must have killed him faster then he could react. Perhaps Soni….

No.

It could not have been Sonic.

But who could have killed him?

"Well, to answer your question. You are, in fact, not dead." A new voice spoke up.

The ninja didn't even wait to register what the voice said. Only where it came from. He turned and swung his sword faster then the eye could see.

"Yikes!" The voice reappeared on Flash's left. He turned and thrusted his sword into a glowing light before it disappeared and reappeared elsewhere.

"Stop it!" The light vanished again after another sword strike. "I said stop it!"

"No! Tell me where I am!"

The light began appearing in multiple places at once. They still got slashed by the ninja because of the speed he was moving. "I will if you just stop! Please!"

Flash's sword stopped an inch from another light. He sighed before sheathing his sword. "Because it doesn't seem like I could kill you, I'll let you live."

The orb was silent for a few seconds. "Huh?"

It then began to take shape. Legs sprouted from beneath and arms grew from the sides. A head slowly rose up from the top, and when it stopped shifting the orb had transformed into a transparent boy. No bigger than Child Emporer.

"Hello, Flashy Flash. I am Future."

Future's head then came clean off. "Are you serious?"

"After all those attacks, how did you not see that coming?" Flash, once again, sheathed his sword.

The transparent boy grumbled before are growing his head. "Okay, fair enough." He cleared his throat. "You are probably wondering why you are here."

"That came to mind." The ninja's patience was never that great. Even when it needed to be.

"You see, after your little stunt, me and my twin, Past, woke up." Future explained.

"Past and Future. Odd names for twins. Wait, what did I do?" asked Flash.

"Your speed test from before ended up breaking time. What the machine recorded was the actual time, but that stunt jumps every living thing, within a hundred meters, .5 seconds forward into time. That is why the machine said you were slower. Because it lost track of you."

Flash looked on with a stare. "Why should I believe that? It sounds impossible"

"That is why my brother and I woke up. A massive force of that energy shook us awake from your interference of the timeline."

The boy sat down crosslegged. "Me and my brother are two entities with power over time. But the downside for me is I can only try to fix the problems my brother causes."

"Past tries to mess with the timeline by bringing someone to the past to change events. He does this to create as much chaos for me to try to correct. And if I fail, then he wins and your world becomes a disaster."

Flash decided to sit down in the grass as well. "So what happened last time you failed."

"The monster invasion occurred. You know. The most important event of your time."

That caught the ninja off guard. "Who did he send back?"

"Not important. What is is that he has a specific part in history he wants to change. And when you broke time, he woke up earlier with limited power. So he went as far back as he could in your life with what he had and grabbed people from your past. Then chucked them into the time he wants to change."

Flash began to nod his head with his chin cupped in his right hand. "So why not send an army back in time, or better yet, Saitama."

"A: I can only send one person. B: I need a swordsman. C. You created this mess, you are going to fix it."

"I'll explain what my brother is trying to change. You see, he wants to keep one of the first monsters alive. Muzan Kibutsuji, or the first demon."

"Demon?"

"You'll figure it out. Also, he wants to kill the main reason for Muzan's defeat. Tanjiro Kamado."

The kid put two fingers in the air and dropped one. "If Muzan lives, demons will continue to kill for all of eternity. The human species will be just cattle to them in due time."

He dropped the remaining finger. "If Tanjiro does. Then so does his sword techniques that his ancestors use to guide survivors of the monster invasion. Humanity will be whipped out."

"Your mission is to aid in the destruction of Muzan and make certain Tanjiro survives."

Flash looked into the sky. "What if he sends someone faster then me from my past?"

"That is why I will drop you at the beginning of Tanjiro's journey. This era has forgotten techniques that you can use to boost your power. Learn them, guide Tanjiro and his sister, Nezuko. Prepare for the battle. Everything lies on it."

Forgotten techniques? This could benefit him. If he could learn these techniques, then he could go faster.

"Alright, I'm in."

Future clapped his hands. "Great. Oh, a few things before you go. You will not age. Save you the trouble of coming back older. Also, don't let anyone kill Nezuko. Regardless of her…condition."

"What?"

"Finally, any positive change in history you make I will not revert. I would actually appreciate it if you did just to rub some salt in my brother's wound." Future slammed his fist together.

Flash reached for his sword. "You know I'm going to try one more time, right?"

"No you won't." Future snapped and Flash teleported into a night sky.

Wow, it feels good to write something new. Especially with a story between mostly non-original characters. Saves me the trouble of describing the new people.

This fanfiction should be easier to follow.