A/N: I am not all that good with the science part of these shows so I apologize for any mistakes I may make.
Disclaimer: I do not own Supergirl or the Flash.
Kara watched as Mon-El's mother turn to dust, a look of victory on her face. She turned to Mon-El to share in their victory. She found him struggling not to cough. Her look of victory quickly turned into one of concern. No. It couldn't end like this. She wouldn't let it. As Mon-El appeared to grow weaker she quickly went to support him.
"Don't worry, I'm going to get you out of here." She told him as she led him off the roof. "Alex, I need you to do something for me." She told her sister through the set of coms that they used to keep in contact with each other when Kara was off being Supergirl. Her sister didn't even hesitate.
"What do you need?" Alex said. Kara told Alex what she needed from her and she quickly agreed. Kara carried Mon-El who had near passed out to the field where she agreed to meet her sister. Alex was already there with the device. "Are you sure this will work?" Alex asked her sister.
"No. But I have to try. The lead poisoning in the air should have only affected this earth so he should be safe to live on Barry's earth." Kara said. Alex nodded as she stood back to let Kara work the device. Kara quickly opened a breach and rushed Mon-El through. There wasn't much time left.
Earth-1
Iris, Harry, Tracy, Joe, Wally, Jay, Gypsy, Julian, and Cisco were standing in what remained of STAR Labs. Jay had chosen to stay for now, without Barry they would be a little lost and having an experienced speedster would help. All of them were unsure of what to do without Barry. The whole last year they had been fighting to save Iris when in reality they should have been fighting to save Barry. Suddenly an alarm went off. Cisco and Harry were immediately in alert mode.
"It's coming from the breach room." Cisco said.
"Do you think that it could be Jessie?" Wally asked. Harry shook his head.
"No, she said that she would stay on Earth-3 until Jay returned." Harry said. They all headed down to the breach room, prepared to fight whatever came through the breach. Two figures jumped through, neither were figures that they were expecting.
"Mon-El? Kara?" Iris said. Mon-El's response was to take a large gulp of air.
"I can breathe." He said. Team Flash and friends looked at him oddly. Kara was the one to explain.
"Mon-El is from a planet called Daxam. His kind are allergic to lead. A rogue group of surviving Daxamites attacked my Earth and we were forced to disperse an amount of lead into the atmosphere that would be harmless to humans but lethal to Daxamites, including Mon-El. I figured that since there was no lead in the atmosphere here that he would be able to live here." Kara explained. Cisco and Harry nodded at her logic. It made sense after all, they had never had any reason to disperse any type of lead into the environment and Mon-El had no problems the last time he was here. Once Mon-El had appeared to recover they moved from the breach room to what was left of the main room. Kara's eyes widened as they walked in.
"What happened here?" She asked as her eyes scanned the room and the group when she realized that there were two faces missing. "And where are Barry and Caitlin?" She asked. The team stiffened not entirely ready to answer those questions. Eventually Iris spoke up.
"I guess we should start from the beginning. As Barry may have told you for the past six or so months we have been fighting against a seemingly inevitable future in which I was killed by a speedster known as Savitar. As you can see we won, but not without a few losses. The only reason I am here is because the man you knew as HR is gone. He used a facial transmogrification device allowing him to look like me and me to look like him. He told no one of this plan as we learned that Savitar was a future version of Barry, a time remnant, created when Barry tried to come back in time and save me. It was a closed loop, a time paradox of sorts, at least until HR sacrificed himself for me. No one knew until it was over. This is his doppelganger, Harry from Earth-2. In order to defeat Savitar in the future Barry trapped him in the speed force and when he escaped, first Wally and then Jay," Jay nodded at Kara so she would know who he was. "took his place. Cisco figured out a way to trick Savitar and set Jay free, which worked as you can see but without a prisoner, the Speed Force became unstable it needed a speedster so Barry sacrificed himself and went into the speed force. I hope to find a way to get him out and stabilize the speed force but that is going to take some time. As for Caitlin, she was injured and in order to keep her alive we were forced to take off the necklace which kept her powers at bay and she turned into Killer Frost. She became detached from her emotions and joined up with Savitar. She eventually turned on him but left to discover who she was now. She knew that she was no longer Caitlin but she also knew that she wasn't Killer Frost anymore. And that's the story." Iris finished. Kara was in shock. She couldn't believe all that these people had been through.
"That's awful. I am so sorry for your loss if there is ever anything I can do to help please come and find me. If you would like and if he agrees I am sure that Mon-El will be willing to help you as well." Kara said. Mon-El nodded at this.
"Absolutely." He said. "Kara, can I speak with you for a moment?" He asked. Kara nodded and they moved outside of the room for a bit of privacy.
"That was really risky and while I wish you hadn't risked, I am alive and am able to still help people. Even if I can't be with you." He said.
"Mon-El, when you were dying, I panicked. I couldn't let you die even if it meant I'd never see you again. I had thought about sending you back up in your pod but realized that I could bring you here and still come to see you occasionally. It was the best of both worlds." Kara said. Mon-El's eyes widened at that realization. He wouldn't have to be separated from Kara, at least not permanently. They would never be able to live together but at least they could still see each other occasionally. Mon-El pressed his lips to hers and she responded in kind.
"I love you." He said as he pulled away.
"I love you too." She said as she kissed him again. Mon-El smiled as they made their way back into the main room and eventually the breach room. Kara kissed him once more as Cisco prepared a breach for her to return to her own Earth.
"I'll see you soon." She said.
Thank You for reading! In the next month or so I am going to write a sequel to this and post it in the Flash/Supergirl crossover section. I will post an Author's note here when I do.
