This was inspired by a fan made video on YouTube I'd watched in which the Flash and Supergirl go to war with each other and I decided to try my hand at it but on a more epic scale and starting with, while involving, speedsters vs Kryptonians. Though it will be set on a different Earth, ones I've made up.

Disclaimer: I don't own "The Flash" or "Supergirl".

Earth-39

Around the world there was chaos and mass destruction as a powerful network called the Guardians waged war against an imperialistic alien race who hailed from the empire of Krypton and were currently invading as part of the latter's plans to acquisition Earth into their empire.

The Guardians consisted of a network of speedsters, each having their own respective uniforms and code names who conducted heroic missions across the world and performed rescues, saved lives, dismantled criminal operations around the world, and were also tasked by the United Global Democratic Collective, the new international governing body that united all the nations worldwide into one country but with democracy as its core rule of law, to defend the world against threats from outside of the galaxy.

The Guardians headquarters were based in Central City and were founded and led by a young speedster named Barry Allen who worked as the chief forensics expert within the Central City Police Department. His code name while operating as a hero was the Flash and his organization included several speedsters such as his foster brother Wally West, Jay Garick, Hunter Zolomon, Jesse Chambers, Eddie Thawne, Eliza Harmon, Edward Clariss, an unknown individual who called himself the Accelerated Man, Danica Williams, Libby Lawrence, his children known as Don and Dawn Allen, all of whom made up the Central City cell, and a multitude of others.

The Guardians were also divided into different cells across the globe and operated on an international scale but always united as one when their world was facing an existential threat like what they were currently facing.

Speaking of which, the invaders were being led by General Kara Zor-El Zod, daughter of Emperor Zor-El and Empress Lyta Zod and cousin of prince regent Kal-El who'd been adopted by his aunt and uncle years ago on their world following the assassinations of his parents Jor-El and Laura Lor-Van El due to a coup attempt against the combined royal houses of El and Zod.

Her brother and Kal's other cousin, Supreme General Dru-Zod, controlled the empire's entire military force and all of the other generals, including Kara, answered to him.

During their conquests the empire had learned of Earth and decided to acquire it in order to expand their reach across the universe, leading to the current predicament, and Kryptonian warships were deployed above all of the major cities worldwide including Cairo, Paris, Rome, Tokyo, Moscow, London, Madrid, and others along with major U.S. cities such as New York, Chicago, and Washington D.C. The lead ship that Kara manned was above Central City.

As the invasion was underway, there were scenes from across the world involving speedsters engaging with the Kryptonian warriors deployed on the ground and using speed punches to send them barreling backwards while other speedsters blasted their opponents with combined speed force lighting head on, the Kryptonians reeling from the highly intense strikes of said lighting.

The invaders on their part unleashed strong, fiery blasts of heat vision towards their enemies who ducked and dodged the blasts at top speeds, though in some cases members of the Guardians were struck in the chest by said blasts and severely wounded or worse tragically killed, and countered by circling their arms and generating tremendous gusts of wind that extinguished the heat vision and swept their enemies off of their feet and flung them away like ragdolls.

Sometimes the Kryptonians heat vision struck the ground and caused small to medium explosions and flaming fires as the two sides battled.

Other scenes worldwide included the speedsters and Kryptonians holding onto each other as they spiraled throughout the skies above and wrestled while trading jabs and kicks and on the ground they raced each other across the streets, leapt into the air and slammed against buildings and caused the glass from windows to shatter and its shards to rain down onto the ground though thankfully no one was hit, smashed against vehicles including those that were wrecked during this war, and engaged in advanced martial arts, intense hand to hand combat, brutal, as in brutal, and bloody beat downs, all enhanced by their speed and strength, and tossed each other in different directions.

The Guardians also did all they could to transport fleeing and screaming civilians out of harm's way and sped them to safety as the explosions and thundering sounds of battle blasted around the civilians while the invading ships above also continuously fired their lasers and missiles onto both the ground and buildings below and left fires blazing and thick grey smoke billowing everywhere, adding to the devastation. In some cases certain speedsters multitasked between the battle and the rescues by each creating time remnants of themselves to protect the civilians while they themselves battled the Kryptonian Empire's forces.

Within Central City, where the battle was thickest, Barry was relaying instructions to his children who were still beside him as the three of them operated throughout the city and fought with all they had while protecting its citizens.

"Alright guys. Libby, Edward, and Danica are currently holding off the invaders attacking both the city square and the downtown area, Eliza, Eddie, Hunter, and the Accelerated Man are providing protection for the CCPD while reinforcing their positions, and Jay and Jesse are in the middle of evacuating Mercury Labs due to the enemy ships bombarding it along with other buildings across the city. I'm gonna need you Dom and your sister to go and rendevou with your Uncle Wally as they work to remove individuals from harm's way. Meanwhile I'm going to go and confront the person behind this invasion and try and end it. Is everyone clear on this?" he informed them of their latest steps and then asked.

"Absolutely," and "Definitely," was heard from Dom and Dawn respectively as they responded with full understanding after which they raced off to carry out the latest task designated to them and hoping that their uncle would be alright when they reached him. Barry meanwhile raced throughout the city and rescued more individuals and engaged in intense battles with Kryptonian soldiers as he searched for whoever their leader was. After some time he finally located her, as in General Kara herself. She was hovering in the air above him, arms folded, and blonde hair billowing in the sky as she observed her forces bringing death and devastation to the city below her, a cold and impassive look upon her face.

As Barry took in her appearance he observed that she was wearing a dark burgundy uniform with a silver belt around her waist and a pair of black boots. And the combined crests of the houses of El and Zod was emblazoned upon her chest.

"I am the Flash, protector of this planet, and whoever you are, your invasion upon this planet ends right here, right now. Either you end this immediately and command your forces to withdraw or face the consequences," Barry sternly called out to her, hands on his hips. Kara responded by looking down at the speedster that dared to address her and instinctively ascertained that he was the leader of the other speedsters opposing her soldiers across the globe.

"Actually it is you that I, Kara Zor-El Zod, demand and in the name of my father, the great Emperor Zor-El, to surrender and for your fellow speedsters to stand down. Our great empire has laid claim towards your planet and neither you nor anyone else shall stand in our way," she responded with an air of imperial superiority to the insolent speedster that dared oppose her.

"No Kara. none of us shall surrender and we will never yield to you nor to your empire but will continue fighting for this planet until our last breath. And if we fail to save this world then rest assured that we will avenge it. Last chance. Surrender now!"

"Never!" Kara growled. "This world is ours and you must surrender immediately!"

"Make me," Barry smirked and she, filled with rage and determination, clenched her hands into fists and lunged downwards, barreling into him which resulted in the commencement of an epic battle between the duo over the fate of the planet.

The two of them fought brutally and ferociously as they spun through the air and exchanged speed punches, strong kicks and jabs, head butts, and wrestled with intensity while neither held back.

As they fought, Kara repeatedly slammed Barry against the side of buildings while he countered by pummeling her with fierce speed punches against her shoulders, stomach, and sides. They later crashed onto the ground repeatedly, creating multiple craters in their wake, and raced each other neck and neck while at top speeds engaged in powerful hand to hand combat, roundhouse kicks, uppercuts, and highly advanced martial arts moves such as Jiu Jitsu, Muay Thai, which included the aforementioned roundhouse kicks, Taekwondo, and other moves.

After some time, Kara extracted herself from their fight and clapped her hands together hard, sending a massive shockwave who's ripples swept Barry backwards at great speed and onto his back hard with a thud while also sending vehicles flying backwards as well and uprooting trees. The Guardian leader groaned, his body aching from the impact. But he refused to give into the pain and knowing he had to keep her attention on him, quickly got up and sped away, causing her to leap upwards and fly after him in a speed race.

The two of them raced throughout the city, Barry running through the streets, along the sides of buildings, and leapt from rooftop to rooftop, yellow streaks of Speed Force lighting trailing behind him, while Kara flew above him and continuously shot red, fiery blasts of heat vision towards him which he ducked and dodged. She also blew freeze breath at him while he in turn threw Speed Force Lighting towards her, the freeze breath and lighting meeting each other halfway and causing the former to dissipate from the resulting impact between the two elements.

Multiple times he threw lightning bolts at her whenever she attempted to use freeze breath upon him and she also began throwing heavy vehicles towards him to which he responded by moving out of the way and also speeding away citizens in their trajectory before they crashed into them. He also caught two of the vehicles and used his momentum to send them right back towards her, one of which she dissipated with her heat vision due to the resulting small explosion of said vehicle in midair, while the other crashed directly onto her midsection and sent both her and said vehicle crashing through the top of an empty skyscraper which was since evacuated due to the invasion.

The resulting impact caused a huge chunk of concrete from the skyscraper to be ripped from the rest of it and careen downwards and towards another building filled with civilians trying to evacuate. Barry moved quickly however and leaping upwards, soared through the air vertically and phased through the concrete, shattering it into pieces and saving the lives of the fleeing occupants.

The vehicle that he'd used against her meanwhile went through the other side of the same building and then crashed back to the ground, leaving it a wreck and almost broken up.

As for Kara herself, who was still inside of the building, she shook herself off from the unwanted impact and dusted herself while feeling angrier than before. She then flew out of the damaged skyscraper and towards Barry who grabbed ahold of her in return and in the air they began super punching and beating each other far more brutally than ever before, leaving dark bruises underneath their clothes and drawing a bit of blood from both of their persons. She later took hold of his shoulders and wrenching him off of her, pushed him downwards hard and fast and sent him crashing onto the ground and resulting in the creation of yet another crater.

Barry at this point knew he had to do something and quickly in order to stop this insane, as far as he was concerned, invader and who was one of the most formidable opponents he'd ever engaged. Thinking quickly, he suddenly came up with an idea and put it in motion by gingerly getting up once more and, following a deep breath, began to run in circles and generated a tornado that started small and then grew and increased in size and height until it was towering almost as high as some of the city's skyscrapers. But he was careful to ensure that it'd be contained so that it wouldn't harm the city but only serve its intended purpose.

The tornado swirling around him while he maintained its structure and composition from its side, Barry drove it towards Kara and used its powerful wind gusts to send her tossing around every which way while spinning her through the air like a spinning top.

As he continued to maintain the pressure on her, another brilliant idea came to mind and he strengthened the tornado and increased its height until it reached the lead Kryptonian ship above the city that she'd manned. Increasing it to its maximum strength but still controlling it so it didn't harm the city, used it to send an enormous gust of wind onto the ship that propelled it away from the city and chased it away and into a desolate area outside of the city.

The ship spun around while the occupants inside yelled and screamed in fear as they were tossed around this way and their bodies fell against the sides and ceiling of the ship. Others held onto different surfaces for dear life to keep themselves from being flung about. Once they were above that isolated area, Barry then used the tornado to hurl their ship upwards and then send it crashing down hard and resulting in a fiery explosion while killed everyone onboard while dark grey smoke from the crash billowed high into the air.

Barry's actions were being broadcast live on television screens everywhere around the globe and witnessing them caused the other Guardian members fighting worldwide to follow his example and they generated their own tornadoes and used them against the warships above their cities, driving them out of the city limits and crashing them to the ground in isolated areas, each of them exploding on impact which in turn put an end to the bombardment from above and ground the invasion to a near halt.

At first there was silence worldwide, no one moving or speaking but standing in shock as each Kryptonian warship was destroyed by the Guardians, who on their part were wishing they'd thought of that tactic themselves while feeling an even deeper and greater respect towards their founder and leader for his brilliance and tenacity. But then roars of rage followed as the invaders still on the ground reengaged with the Guardians and fought more ferociously than ever before while resuming their attacks but without the aerial support.

Back in Central City a very loud "NOOOOOOOOOOOO!" was heard from Kara, enraged at the destruction of her fleet and her ship especially. And as soon as Barry returned to the city and prepared to reengage her, she grabbed ahold of two Kryptonian swords lying on the ground next to her which had been left behind by one of her soldiers who'd earlier been using them in a battle with the Guardian speedster Eddie before the latter disarmed him of them and they'd continued their fight elsewhere.

Afterwards she then charged at him and then began slashing her swords against him with broad strokes at super speed while spinning and twirling with a deadly elegance. Barry in turn weaved himself around the swords as they attempted to slice or stab him, speed vs swords, while bending his upper torso sideways, backwards, and around. This continued onwards until he, in a move taught to him by his close friend Oliver and the latter's wives Nyssa and Sara, the three of them co leaders of another organization known as the League Of Shadows who's purpose was to eliminate the worst of the worst in the world to maintain balance against darkness, disarmed Kara of one of her swords and began an epic sword fight between them.

Speaking of which, but he'd also received instruction in sword combat from his three aforementioned friends.

Their swords clashed together with strong sounding clangs as they moved them upwards, downwards, backwards, and forwards in a dazzling display. As they continued to fight and their swords battered together intensely, they each kept trying to gain an advantage against each other but both were moving too fast for either of them to find one.

The sword duel continued for a significant amount of time until Barry, having had enough and finally seeing an opening, directed an open hand jab against Kara's throat, causing her to reel back in surprise and gag. Quickly moving before she could recover, he used his other hand to wrap it around her wrist tightly, the wrist who's hand held her own sword, and twisted it until the sword fell out of her hand and fell back to the ground.

Finally, he wrapped an arm around her neck in a chokehold and lifting up his sword, held it above her heart.

"Yield general. All of your warships invading our planet have been destroyed and you are now at my mercy. This is our planet, our people, and we will defend it with everything we have and as the protector of this planet I command you and your remaining forces to withdraw from this planet immediately to never return or I will run this sword through your heart. AM I CLEAR?!"

Kara was stunned and shocked by what had just happened. Never before had she been beaten and the idea of it happening was inconceivable to her. Never once had she lost a battle and especially with the training her brother had put her through and she'd always succeeded in conquering multiple planets for the glory of the empire. Yet now here she was, General Kara Zor-El Zod, defeated and at the mercy of the chief Guardian protector who was literally the guardian of this world.

While furious about this turn of events, Kara knew she had no choice but to concede that she'd lost since while her people were ruthless, power hungry conquerors they also had a strong code of honor in which they were required to relinquish their claim on a planet they wished to conquer if that planet's inhabitants, protectors, or chosen champions bested them. And the Zod side of their family's code taught that while they must fight with pride and without mercy, they must also fight with honor. Honor above all.

"I yield Flash. I yield," Kara groaned in defeat after which Barry let her go and she stumbled away from him, rubbing her neck gently.

"Now take your forces and leave and never come back to this planet ever again or it shall be your end," Barry commanded her. She glowered at him and then pressing a button on her arm, brought forth a beam of white light which enveloped and transported her and each of her soldiers from every corner of the globe and upwards into another warship much larger than hers and was hovering above the Earth's atmosphere. That ship happened to belong to her brother, Zod himself, who'd been observing their invasion through monitors on his ship which was accessed from the feed of the other warships before they'd been destroyed, and he was none too pleased by his sister's defeat but as per their code had no choice but to retreat.

Once she and her men were onboard, her brother severely and loudly chastised her for their defeat while her head was lowered in shame and he also backhanded her to boot though his great disappointment in her hurt far worse than the strike and she'd have to live with the fact for quite some time that she'd been overpowered which in turn would temporarily see her reputation across the empire in shatters.

Back on Earth, everyone around the world cheered and rejoiced now that the invasion was over and they no longer had to run or hide in fear. It was a bittersweet moment due to those who'd perished and especially for the Guardians who'd lost many of their comrades in this war and there were plenty of somber moments for everyone. But they and their fellow humans would always remember their losses and honor the memories of those who'd perished.

In Central City, Barry was exchanging hugs, handshakes, and backslaps with his fellow Guardian teammates including his family among them such as his children and Wally, other close friends such as Cisco Ramon and Caitlin Snow who were his closest friends, and also his foster father Joe West, Wally's dad, who emotionally embraced both men tightly, crying over them and feeling great relief that they'd survived. And he did the same with Dawn and Dom, having been feeling scared like crazy when he saw them battling the Kryptonians and knowing he never wanted to see that ever again. His family was just too precious for him to lose.

And shortly afterwards, as Barry held his twins in his arms, the three of them wrapped around each other in a group hug, both of them looked up at him.

"You did it dad, you saved us all," Don spoke while staring up at his father with love and admiration.

"Yeah dad. You're the hero," Dawn agreed and smiled at her father with all of the love she could muster. Barry however shook his head.

"No guys. We all did it. We all fought for this world and you both are as much heroes as I am and never forget that," Barry countered and pulled his children in closer while staring at them with strong fatherly pride, vowing to always fight for them, his loved ones, and this planet no matter what threat comes against it.

A/N What did everyone think of this and of my version of an intense and hopefully epic battle between a speedster and a Kryptonian? Please let me know in the reviews if you want.

This fic isn't over however and as per my summary though not anytime soon, I also intend to write a second chapter but reversed in which, and in another alternate universe, Kara will be the hero while a Russian version of Barry will be the villain.

On a side note and while I can't remember every single action storyline I've written here, I think this might be my biggest action oriented story I've ever done. And I intend to go even bigger than that in the future. I don't usually reveal previews for upcoming works but in acknowledgement of the upcoming "Godzilla vs Kong" film, I'll someday be writing my own version of a battle between Grodd and King Shark but with Grodd as the hero and King Shark as the villain while the former will be backed by the Gorilla City apes and the latter will be backed by a small army of giant man sharks like King Shark.

Finally, the character Lyta Zod and the Zod family's code about fighting with honor, pride, and without mercy is from the now canceled series entitled "Krypton". Though Lyta is Caucasian looking in this universe.

Have a great day.