I promised I'd always protect you... (Supergirl/Arrowverse Crossover)

Chapter 1- It begins

So I'm super nervous to post this story but I've written it all so no point in backing down now. Anyways, I'll post new chapters at least once a week maybe more often, all I know is I'm going to do my best. Still, this is my first story that is not related to the general plot of the show, and by that I mean it's not based off an episode at all. It's also more than one chapter which I've never done before or posted at least so please be nice but I still welcome helpful notes/comments. I hope you guys like this. 

Disclaimer: I don't own any of the arrowverse/DC/CW characters, story lines, or really anything to do with them. This is purely fanfiction written for the enjoyment of others. 

Earth-38 National city.

Kara was flying over her city one last time just to ensure that everything was alright and nothing beyond the police's ability to handle was occurring. Satisfied she flew home and through her loft's window landing on her couch.

"Someone looks tired." Alex says, standing behind the island unpacking the take out food which was of course potstickers. Kara spotted her favourite and immediately perked up.

"Yeah, a lot happened today but it was all worth it for potstickers!" She chirps, now grinning. Alex gives a light laugh before handing her sister some food. Kara walks over, placing her plate on the living room table and quickly speeds into her bedroom emerging in some more comfortable clothes. Alex is about to join her sister on the couch when she sees something written on Kara's hung up calendar.

"What's this?" Alex asks, pointing to the date that was only 3 days away. The writing in the little box read: Supers get together.

"Oh, Cisco sent an invite about a week ago. Thought it was about time we all got together when the world wasn't being invaded by aliens, attacked by Nazis or when I'm in some weird musical coma." Kara responds, causing Alex to smile.

"You guys do have a great track record." Her sister chuckles and Kara playful pushes her shoulder. "Still, it'll be good for you guys to see each other. All the great work you do and you barely get a chance to just relax." Alex says, taking a bit of her dinner. "Not to mention the different earth thing makes it hard for you to see them." Kara nods, attempting to hide just how happy she was to not only be invited but just to see them all in general. On their earth Kara and Clark were the only superheroes while on earth 1 there was team arrow, team flash, the legends and even rumors of someone called batman. The point was their world had many heroes and therefore a great group of people to reach out to, people who understood what the hero life was like... Kara didn't really have that.

"I'm not going to lie Alex, I can't wait to see all of them. Barry with his stupid grin and Cisco with all his pop-culture references that I don't always understand. Iris, Felicity and Ray's upbeat personalities, Dig and his disbelief in how weird things are getting for him. I even miss Oliver and his brooding." Kara laughs, before elbowing her sister. "Plus I think they'd like to see you again too, I know Sara would." Kara adds and it's Alex's turn to playfully shove her sister. The conversation stayed on another earth for a while until the topic slowly changed, the two Danvers sisters were just happy to have a peaceful night for once, a night they really enjoyed.

The next day at the DEO.

"Hey Winn." Kara greets her friend as he spins around in his chair to face her. Kara is once more in full Supergirl attire and Winn smiled at his cheery friend. "Nothing going on still?" She asks. Kara was suspecting something to have happened by this point in the day, but for some reason National city was peacefully calm.