Harry Potter is the property of J. K. Rowlings and Supergirl the CW. I own nothing and I don't make any money from this story.

Prologue: He is DEFINITELY not the Flash

"W-what are we gonna do?"

That was the question on Alex Danvers mind as she put her phone in her pocket. She had just lost contact with her girlfriend Maggie who was under attack at the Police Department. Their home, National City, was currently being invaded by a race of aliens called Daxamites. Who last night had parked a fleet of spaceships in the sky above their city and minutes ago had opened fire and began transporting troops into the streets.

Standing in the nerve center of the Department of Extra-Normal Operations, the resident technical genius and super fan of all things alien was Winslow Schott Jr., known to his friends as Winn. He had been trying to monitor what was happening in National City in an attempt to coordinate the efforts to defend their home. But was stalled as a broadcast appeared on every computer and digital device in the city. It was a message from the leader of the Daxamites, Queen Rhea, proclaiming this planet to be New Daxam and that they come in peace.

Winn had just turned from his terminal, reporting the crash of their satellite monitoring network to Alex, to ask that most important question. 'What are we going to do?' Alex wondered, as the situation seemed to be spiraling out of control.

Before Alex could even finish the thought, sudden bursts of light on the upper catwalk preceded the arrival of Daxamite soldiers inside the DEO. Another burst of light not one second later, brought one more soldier landing on top of the central table. Alex and Winn, who had been standing right at the edge of the table, suddenly found themselves not two feet from an armed and hostile alien invader.

"No, no." Exclaimed a suddenly alarmed Winn.

But in the split second it took for the Daxamite to aim his weapon at them, Alex had already drawn her sidearm and fired a shot of blue energy right into the chest of the soldier. At point blank range, even the body armor favored by the Daxamites didn't offer much protection.

Sparks began flying as the other soldiers in the room quickly began firing on all DEO agents who didn't react as swiftly as Alex. Grabbing Winn (the only unarmed person in the room) by the front of his shirt and pulling him under the table for cover. Most likely saving his life.

Alex looked around the room and quickly assessed the situation. Caught completely by surprise, the DEO agents were falling like flies.

With their director J'onn J'onzz currently out of action, as the number two agent at the DEO Alex was in charge. Falling into the role she had been trained for she assumed command of the situation.

"Everybody evacuate!" She shouted.

"Go, go." She urged Winn who was still crouching behind the central table. Gesturing for him to make his way away from the weapons fire and towards the nearest exit. Heeding her instructions Winn made it two steps before turning back to grab his portable tablet terminal off the circular table he had just been crouching behind. Knowing that if they were going to mount any sort of counter offensive they would need access to the DEO's alien database.

"Supergirl we are under attack." Alex shouted knowing the communicator in her ear would pick it up over all the noise and weapons fire.

Supergirl was the name of the DEO's alien celebrity and recruiting poster girl (if clandestine government organizations had recruitment poster). She is also one of the last survivors of a race known as Kryptonians, and under the light of earths yellow sun was one of the most power individuals on the planet. As well as the self appointed protector of National City and all who lived there.

She is also known as Kara Danvers. Alex's adopted little sister and her favorite person in the world.

When Kara was a little girl her planet Krypton was dying. Her parents put her and her baby cousin Kal-El into spaceships before their planets destruction and sent them to earth in an effort to save their lives.

Unfortunately for Kara, her pod was knocked off course and she became trapped in a dimensional prison known as the Phantom Zone. The less said about that place the better.

By the time her pod finally made it to earth her cousin Kal-El had already grown up to become the earth's mightiest protector: Superman. He placed Kara with the Danvers family in an effort to give her a normal childhood like him. And for several years Kara endeavored to live her life as fully, but also as normally, as possible.

As Supergirl, she is the DEO's most prominent figure, and their most cheerful and optimistic agent. For almost two years now she has helped the DEO, alongside her sister Alex, protect the world from alien threats. But as Kara, she is a reporter for CatCo Worldwide Media, and the former assistant and protege of the queen of media herself: Cat Grant.

She is also the girlfriend of Mon-El the prince of Daxam.

Mon-El arrived on earth several months ago after his pod crashed in National City. After Krypton exploded and its remnants rained down on Daxam, his home planet had been rendered uninhabitable. Believing himself to be the sole survivor of his species Mon-El began to carve out a life for himself on earth. And despite a few cultural misunderstandings and character flaw driven mistakes, that made Kara almost want to strangle him, he had found a home for himself.

However, that was nearly ruined by the arrival of his parents. In helping Kara and the DEO break up an alien trafficking ring, he had come to the attention of some of Daxam's allies. Who quickly reported his location to the king and queen.

After failing to drive a wedge between Kara and Mon-El in a ploy to make him leave the life he had built on earth, Mon-El's father agreed to take their ship and leave the planet in peace. Unknown to Mon-El, Kara, and the DEO, Queen Rhea was not content to leave her son behind, and had since then had been working in secret on a means of bring the other survivors of Daxam to the earth. After murdering her husband the king for what she perceived as a grievous betrayal.

Which brought about their current situation.

"I've evacuated the DEO." Alex continued.

"Hang on I'm almost there." Kara responded. One arm stretched out in front of her as she flew as fast as she could. Pushing her super speed to the limit in an effort to arrive in time to help.

"There's no time."

"Alright I'll meet you outside." Kara replied.

Realizing what her sister meant Alex fired another shot at a Daxamite soldier charging her position and began to run toward the far side of the room and the balcony that overlooked the city. Quickly dropping to one knee and sliding under the weapons fire of another soldier attempting to stop her, Alex jumped back to her feet and ran full throttle towards her only chance at escape.

With more soldiers teleporting in behind her, she knew the chances of making it over the edge without getting shot were slim. Seeing a hole in the concrete railing around the balcony, Alex leapt into the open air. Before gravity completely took hold she twisted mid jump, brought her sidearm around to the pursuing soldiers and fired a shot right into the middle of them. Before the edge of the balcony obscured her line of sight, Alex was able to see that her shot caught her target dead center in the chest plate sending him sliding halfway back across the room she had just sprinted across.

Flailing her arms and legs as she rapidly descended the skyscraper, she was able to turn to face the oncoming ground. From her left Alex could see the red and blue blur of her sister barreling to her rescue before she met her end on the pavement below. But had she looked to her right she would have seen the blue and white circle of light of a breach in the multiverse down the street. More importantly the sudden burst of silver lightning that shot out of it.

'This is gonna be close.' Alex thought.

Just as her sister was almost between her and the fire truck on the street below her, a bolt of silver lightning seemed to travel from the street, up onto the fire truck, and spring to Alex before Kara could touch her. Before she was even aware of what was happening Alex felt a sudden lurch in the pit of her stomach, then the feeling like being inside a wind tunnel and then she was back on the balcony she had just jumped off.

Kara flew up and was at her side a second later. "Alex wh-"

Kara didn't get to ask her question before her sister spun towards the corner of the balcony and keeled over. Momentarily stunned by this sudden action Kara waited for Alex to finish gagging before trying to address her again. "Are you okay?" She asked as she placed her hand on her sister's shoulder to steady her.

Wiping her mouth on her sleeve Alex turned to Kara, "yeah, I think so."

"Okay, then maybe you can tell me what just happened?"

"What do you mean what just happened?" Alex responded, looking around at the place she had just left. "And why did you bring me back up here?"

"That's just it Alex, I didn't bring you back up here." Exclaimed Kara. Concerned over what had just transpired.

"What are you talking... Wait, why aren't we being attacked." Alex asked, shifting gears mid sentence.

"Attacked?" Kara questioned, stumbling over the sudden change in the conversation.

"Yeah, attacked. I just evacuated the building because dozens of Daxamite soldiers were storming the DEO. And they were right behind me when I jumped over the ledge. They should be all over us right now."

Seeing her point, Kara turned back to face the inside of the build to be confronted by something truly bizarre. Of the soldiers who teleported into the DEO half of them were on the ground either unconscious or worse. All of them with severe gouges in their armor and lacerations on their arms and chests almost like some one had slashed at each of them several times with a knife.

The soldiers still standing seemed to be trying to attack what looked like a bolt of silver lightning flashing from one end of the room to the other. Engaging various soldiers at random. Presumably in an attempt to keep them off balance.

"Is that a speedster?" Alex asks as they move further into the command room. Watching the devastation of the Daxamite warriors as they failed to mount a defense against this unforeseen enemy. One soldier on the catwalk overlooking the room was trying to get a bead on their new opponent but only managed to miss and shoot one of his own men as the lightning moved in front of him. Before traveling up the stairs to take his weapon and whack him over the head with it. Sending him tumbling over the railing down to the floor below before going back to attacking the other soldiers still standing.

"Your friend the Flash couldn't have picked a better time to come for a visit. We could sure use the help." Alex stated. Suddenly much calmer in light of her sister being here and the fact that the Daxamites were to preoccupied fighting off a lightning storm to even realize they were there.

Kara however, didn't share her sisters enthusiasm in light of one glaring problem.

"I don't think thats the Flash." Kara expressed her uncertainty.

"What do ya mean? Why not?" Alex questioned, trepidation entering her voice over this statement from her sister.

Kara couldn't blame Alex for not understanding. As far as she knew the only person who could move as fast as her cousin was Barry Allen, the Flash. A speedster from earth-1 in the multiverse who had accidentally jumped to their earth about a year ago and helped to apprehend two dangerous meta-humans, Livewire and Silver Banshee. But Alex had been on the run with J'onn from the DEO at the time and had never had the pleasure of meeting Barry, though she had certainly heard a lot about him after he left. Barry had appeared again just after thanksgiving to ask for her help with an alien invasion on his own earth. Kara had been happy to help, but Alex stayed behind and thus never got the chance to meet Barry, or his friends and see them in action.

Her doubts about this being her friend were caused by what she was seeing. First there was what was done to the Daxamites. For all his resolve to fight the good fight, Barry was a kind person and a gentle soul. He might not have a problem punching his enemies until they were unconscious, but he would never cause some of the damage she was seeing here.

Second, was the lightning that was still zipping around the room. It was silver. When Barry ran he left a trail of yellow lightning in his wake, not silver.

But most unusual of all was the fact that Kara couldn't see the speedster that was doing this. "What do you mean you can't see him." Her sister asked after stating this fact. "You mean this speedster is too fast for even you to follow?" Alex exclaimed with equal parts admiration and alarm of an unknown speedster her sister apparently couldn't keep up with.

"No, I can follow the lightning just fine." Kara clarified. "I mean I literally can't see the speedster in front of it."

"What do you mean? That he's invisible." She exclaimed with incredulity.

"Yeah actually thats exactly what I'm saying."

"An invisible speedster," Alex mused. "Now I have seen everything."

"Technically you haven't actually seen him yet." Kara proclaimed with some humor. Finally taking her eyes away from the battle in front of her as the last Daxamite went down. Turning to her sister, Alex was about to admonish her for making jokes at a time like this, when they were both distracted by shouting behind them. One of the unconscious Daxamites they had passed on the way in had apparently woken up and was now point a weapon at them.

Alex drew her sidearm from its holster as she turned to face the new threat. Kara moved in front of her in an effort to shield Alex from any lethal fire when the soldier abruptly went ridged. He dropped his weapon as his arms fell slack at his side and his feet left the ground as he slowly rose in the air. Kara and Alex were both stunned by this until a figure began to materialize in front of them.

It was the speedster. Or at least, Kara assumed it was judging by the suit it was wearing. It seemed to be the polar opposite of her friend Barry. Where his suit was bright red with gold lightning bolts around his waist, arms and legs. This speedster seemed to prefer the darkest black, with bands of silver. Barry also left his eyes and mouth exposed, this speedster didn't seem to have an inch of exposed skin. Even his eyes were blocked by some kind of white lenses so Kara couldn't even tell what color his eyes were. And unlike Barry, who wore his white and gold lightning emblem on his chest, this speedster had no such symbol. The closest he had was a silver necklace with what looked like animal claws hanging from it. Bringing to mind the totem necklace worn by Amaya (a.k.a. Vixen of team Legends).

This speedster was at the moment staring at Kara and Alex while holding the Daxamite soldier over his head with one arm. A moment later he tossed the man aside. They watched as the body came to a stop against the wall. Alex and Kara both noticed the blood stains and puncture holes in his armor. Turning back to the mystery speedster they could see blood dripping from what looked like metal spikes on his fingertips.

Kara couldn't seem to take her eyes off the man before them. But Alex quickly looked back at the other soldiers and assessed them with a more critical eye. Now taking notice that all of the lacerations on each body ran parallel to each other, and that they were about finger width apart she came to a startling conclusion.

'They're not knife wounds. They're claw marks.'

Turning back to face this possible new threat Alex only had a moment to stare before he once again turned invisible and a quick flash of lightning out the window signaled his departure.

Hoping for some kind of explanation as to who that was and what just happened, Alex turned to meet the eyes of her sister. Lifting her eyebrows in a silent prompt for Kara to say something.

"He is definitely not the Flash."