A/N: Well here we go! This is my third year of running these '100 days to...' stories, the first year for Supergirl, last year for the four series of the Arrowverse. Last year I did it as smaller, separate blocks, but this year, because ambition got to me, I decided to make it a single, 100-day/chapter story. And I decided to craft myself a big ol' alternate universe, enabling me to start planning toward it well in time. So I've been preparing for this since last fall and now it's time to start! Of course, you may have seen the series of single chapter stories I've been putting out over the past few months, the 24 'Preludes,' giving you a peek into this other world (I highly recommend going back to check them out, for further information and lead up to this story.)

The only other maintenance issue left for me to pass on has to do with the posting format. As it's not possible for me to create a story marked as crossing over between all four of the shows, I've split it into two volumes, one under the heading of The Flash and Supergirl, the other under the heading of Arrow and Legends of Tomorrow. The odd-numbered chapters will be in the former, the even-numbered in the latter. The easiest way to follow the story would be to put in for notification on both. Now on to the story!

ONCE MORE UNTO THE BREACH
Day 1 of 100

Volume 1, Chapter 1

Location:
BREACH EARTH, HAVEN QUARTER
(ARGUS designation)

It had been just over two years now, from the day where she had been deposited back in the place where she had lived for the first fourteen years of her life. This was the place where she had been Kara Danvers, daughter of Jeremiah and Eliza, sister of Alexandra. This was the place where she had grown up, until the day where an incident had left her propelled into another world, just clinging to life, until she'd been found by a pair of scientists who had taken her broken little body and carried it to safety, fixed it, until she awoke and found… she had no memory of who she was, not one thing. Well, one thing. She remembered her name. Kara. Even now, all those years later, even after being back here for all this time, everything that came before her being tossed through a breach from her home in what they called Haven Quarter to the one called War Quarter was just gone.

Her mother, her sister, they both tried so hard to get her to remember, showing her pictures and videos, objects… They shared story upon story, and always they would get this look in their eyes that said 'oh you have to remember this, of course you do, because you're Kara. You're our Kara, you know this.' And much as she knew that they meant well, that they only tried so hard because they had faith in her, all she could feel was her own frustration rising. They tried, and they tried, and she did, too, honestly. But it just wasn't there for her to find, and the more they tried, it sometimes got to feeling like she wasn't enough for them. It made her think that she could never be Kara Danvers again, that she was now and forevermore Kara Zeta, the adopted daughter of Laura and Eliot Zeta of War Quarter, or as the people had come to know her… Black Siren.

She hadn't told her mother or sister about this ability she'd gained following her time with the Zetas. She didn't know why she'd bothered to hide it at first, especially when she still felt nothing toward them. They had recognized her, but she had no memory of them at all. But… they had such emotions when they saw her, when they saw that she was alive, and well, and grown, and even though she didn't know them, she knew the difference between genuine and fake reactions. They were just so happy to have her back… What if their finding out what she'd become took away that hope she'd just given them? So she hadn't told them. Even so, back where she'd come from, she had used her powers to help her help the people of her quarter, of her city, and that drive hadn't been left behind.

And so, the Black Siren had started to do her part around this new city. Not that the transition had been an easy one. She had come from a world of pain and destruction, of fear and hatred and been dropped into… colors and laughter, and peace and quiet… No wonder they'd called it Haven. Of course, it wasn't all sunshine, or else she'd have had little to do as a heroine. But then there would just be times where she would look at this place, this generally calm place and think how none of them had any idea how good they had it, and it would frustrate her. And then at other times… she would look at this place, this peaceful place, and she would know: she would protect the Haven from anything or anyone attempting to harm it or its people.

For how little anyone could regret the world she'd left behind in returning here, Kara could not pretend as though there weren't things she did miss. For all the grief it had caused her in the end, she did miss Stein Labs and the man behind the place, Martin Stein. She missed the friends she'd made, hard earned as they had been. But most of all, most of all she missed her parents, and their little home. She had not seen them since she'd come back through that breach, and she often ached to think of them out there. With how suddenly she'd gone, she'd never gotten to say goodbye, and they'd had no idea she was leaving. Did they think she'd died? Had they been looking for her? Had the war reached them? Were they still alive?

She had returned to the place where she'd been born with the aid of a girl known as Seeker. If not for her, she would still have been out there, with her mother and father. Maybe things would have gotten better between them if she'd stayed… or maybe they would have gotten worse. She hadn't seen Seeker since the day she'd walked her through the breach out of War into Haven and, wishing her good luck, she'd left her there and disappeared again. Two years, three months, seventeen days and some hours… And then the counter had been turned back down to zero.

Out in the city at night, high above and looking down from some roof or another, Kara could almost forget if she was in one quarter or another. Here she was just in her city, and she watched over it, waiting to catch on to something, some sound or sight that would tell her… she was needed. That night, there was something in the air, like an invisible presence… very near, almost… behind her?

Turning at once, ready to unleash a cry that could propel whoever was trying to sneak up on her far across a city block, she found… nothing. She frowned. The feeling was still there.

"Show yourself!" she called, even as the sky rippled and surrendered the shape of the dark-haired girl. "Seeker?" She could as easily have maintained her stance, not knowing what would bring her here on this night or any night after all this time, but for all the times she'd thought about the place where she'd made all the memories she still had in her life, and all the times she'd had to remind herself there was no way back, not without whatever had sent her there in the first place or without the one who'd brought her back, all she could do now was to relax and stand up straight once again. "What are you doing here?"

"Well, if memory serves me right, when I brought you home there was talk of you owing me one?" Seeker had declared, walking up toward her. "If you're not too busy, I think I need to collect on that."

X

MAIN EARTH, THE CITY BENEATH THE BREACH
ARGUS HEADQUARTERS

Dinah Drake knew better than to act in haste when bringing this matter before Director Heywood. They all dealt with breachers on an almost day to day basis, it was part of their job to recognize potential threats, whether they could affect their own Earth or the one across the breach, and to ensure they never got to be carried out. And this one… This one could be seen as little more than an inkling, as getting ahead of herself, but off of what little they did know… well, here she was. Here they were.

"Thank you for coming, Detective Raatko," Dinah held out her hand to the woman as she was escorted through.

"Nyssa, please," she'd replied, shaking her hand and telling her how she'd just come from interviewing one last minute source. "Ready when you are."

Dinah wouldn't have gotten to this point, she knew, without the detective's help. Nyssa Raatko was known for being at once respectful toward and respected by those breachers who'd made the crossing on to their Earth for the sake of escaping the circumstances of their home quarters. And for that she had grown to be seen as an ally within their circles, someone who would help them settle somewhere without drawing attention to themselves, who by reputation alone would be heard if she came calling. Dinah had called on her for that reason, as well as the fact that she'd already caught wind of some of the situation in a previous encounter.

Some months ago, Dinah had come to witness an exchange which took place, between two girls out of the quarter designated as Mist and three women out of the one called War. The Mist girls had handed something over to the War women in exchange for forged documentation that would allow them to settle on Main Earth. The women and the item they'd traded for had been apprehended, while the girls – with Detective Raatko's aid – had been settled somewhere safe after having told the nature of their trade, but even so… Now they knew what the women had been after, and it set the ARGUS agent on the investigation which now brought her and the detective to the door of Henry Heywood's office.

"Agent Drake, Detective Raatko, please," the director motioned for them to sit across from his desk as they were let into the office. The women sat, and the director gave a nod that told them to proceed.

Despite its potentially inoffensive sounding designation, Mist Quarter was by no means quaint. On sight alone, maybe, like in a photograph or video recording, it might have seemed normal enough, in need of a bit of embellishment, some tender care, sure, but then you would see its people and you would start to see something wasn't right. Why the masks? And then you would start taking a closer look at that image, notice the lack of greenery. If you should be so unfortunate as to then find yourself in Mist Quarter, you would know at once why it had gotten its name as soon as you breathed its air. The ARGUS agents who had found themselves posted in that quarter certainly didn't look to it as the opportunity of a lifetime. It felt a lot more like punishment.

The air would not so soon kill you, no, but the longer you were exposed, say if you spent your whole life there… Even a short exposure would not go without leaving symptoms, which left its residents on a continual battle against their own air. They had their masks, and their homes could count on decontamination and filtration to give them some peace of mind, though it was by no mean a fix. And then there was the water.

That was what the Mist girls had traded to the War women for their new identification papers. Water from their quarter, so little wanted, so easily attained. How could they not accept the trade off? All they were told was that there was some way to make the crossing, and they would be met on the other side by these women, who wanted little more than the water in exchange for making them the papers they needed, wanted it to run experiments, which perhaps could lead to some breakthrough that might help fix some of the great wrongs of their own quarters. Never was it questioned why these people wouldn't make the crossing themselves if they were aware of the way in and out, or why they would be in contact with anyone who could provide these papers. Never did it occur to them to wonder if they were really using the water they said they were, or where they came from.

In the time since she'd become aware of this trade, Dinah had made some effort in relaying what she'd found, but as of yet nothing had come of it. No one seemed to grasp where this could go. So she'd continued looking into it, only privately, until she might be able to bring it to the director, as she did now. For that she had recruited Detective Raatko, asking her to put out some feelers, where she could, see if she heard anything more about water trades out of Mist, and the involvement of War. The detective had done just that, bringing back the information she now submitted to Heywood.

The trade they had interrupted, as they'd learned, was not the first, which they could plainly have expected. In fact, the breachers out of Mist could recall whisperings of 'water for papers' for more than a year, maybe two, although more often than not they had ignored them, never believing that it could be so easy, that it clearly had to be a trick. But there were others, as trusting as those two girls Dinah had met, who had performed the trade, gotten their papers and settled into their new lives, which meant that even though they had managed to foil one exchange, it was only one instance. Whoever wanted to use that water had already gotten their hands on some of it before. They were already doing whatever they intended to do with it, and while there had been no sign of their using it in any kind of attack as of yet, it was Dinah's opinion, and Nyssa's as well, that it could all change before long.

Thankfully, it was also Director Heywood's opinion. After hearing out the two women, taking in everything they had gathered so far, he had agreed to send out the Waverider and its team to investigate the matter. Dinah had known well enough this would be the course of action, and much as she would have liked to see this case through, she simply thanked the director and escorted the detective back out of his office. Snart and his team, they would be able to follow the trail through both Mist and War Quarters and, with any luck, put an end to this before it had the chance to become anything more.

"Do me a favor, keep your ear to the ground out there?" she'd told Nyssa before they parted ways. The detective met her request with an understanding nod, and off she went.

X

Kara had been told, once, about the existence of this other Earth, and even so, being here, it had taken her a little time to really comprehend what it was she was seeing. It looked a whole lot like Haven, it did, but eventually she had gotten to a point where she could look at the city around her and understand… it really was a whole other place. What really set her on track with it, strangely enough, were her powers. It was all about sound, this thing she could do, not just manipulating it but really feeling it out… Over time, she had developed something of a skill in using her ability to extend the reach of her hearing well beyond reach, and, being here… it all just sounded like another place, not Haven at all.

It was also this skill of hers which inevitably became useful to herself and Seeker. They didn't have to break into ARGUS to get what they were after. They only had to stand somewhere, well out of sight, where Kara might stop and listen.

As Seeker had explained it, she'd been scoping out Main Earth, as she would from time to time, to look after some people she'd helped across the breach from their Earth, from War Quarter. She could do that, Seeker. She could feel out where the breaches were, she could move from one place to another in this way, and she'd been using this ability to help people get away, every so often. It wasn't so clear cut, she couldn't just grab loads at once and simply drop them off on the other side, they had to think of the big picture. Either way, she had been here, and in her rounds, she'd spotted the detective.

Seeker knew her by reputation more than anything, but as she trailed after her, curious to see what she was doing, she'd found her talking to someone she recognized. It was a young man, and she recognized him. She'd been to Mist before – with some luck, knowing to bring a mask – after hearing about the place. After her own quarter, this one ranked right up there with some of the quarters she'd seen one was most likely to want to escape, and why should she only help her own people? This young man talking to the detective, she'd almost helped him cross, but then he'd changed his mind at the last second. Clearly, he must have changed his mind, and found another way across.

She'd managed to overhear part of their conversation, only enough to hear one thing… water from Mist…

She'd followed the detective after this. She wasn't sure why she did it, but then when following the woman had taken her straight to ARGUS headquarters, all at once it felt like she needed to make a decision and quick. Something about the whole situation just nagged at her and she had to know. Thankfully, she so happened to know someone with the skill to help her reach a place even she couldn't get to, and fast. That had taken her, as fast as she could, across to Haven on Breach Earth, to find the girl she'd helped cross back to where she belonged a couple years before, the girl who'd told her about these powers she'd developed over in War. She'd spirited her away, back to Main Earth, back to ARGUS, and there they'd stopped, and Kara Danvers, the Black Siren, had listened.

The information she relayed had some effect on the both of them. Kara may not have been born to War, but it was all the world she'd known after losing her memories of Haven, and she didn't want anyone developing some new weapon to go after the people she'd cared about, who'd taken her in, any more than Seeker did. Kara did not know a whole lot about the young woman, but as the two of them took in what she'd just heard, she knew they had one thing in common. They both needed to do something about this.

"What do we do now?" Kara asked her. "What's the Waverider?"

"I know them, this is good, better than them sending out any outpost agents," Seeker promised her. "They're good, and they just might let a couple War girls like us give them a hand. What do you say?" Kara met her grin with a smirk.

"I say lead the way… Seeker," she pressed on the name, showing a curiosity without asking.

"It's Lena," she revealed. "But let's keep that between us."

TO BE CONTINUED (tomorrow, in Volume 2)