*Levi's POV*

"I've been trying to catch her sneaking out for weeks, now, Erwin, but it's like she knows when I'm awake and watching for her. I can never catch her when she's leaving, it's always when she comes back."

Levi paced slightly in front of Erwin's desk out of agitation as he stressed why, after all this time, he still hadn't managed to follow her into the Underground and see what she was doing.

"Do you at least know when she usually sneaks out? The time, or the days?" Erwin asked calmly.

"It's always when everyone's asleep...and it is fairly regular. Every week, I think, though the exact day varies."

"If you can't follow her, then you'll need to get ahead of her. Get down there before her. You know the window of time when she'll be down there, and you know the Underground."

"But I have no idea what she's doing down there. It could be anything–and the Underground isn't a small place where I can wander around and hope I run into her."

"Then narrow down your search based off your theories. We considered she might have family down there, so you would be looking at residences, or asking around about a woman of her description. And your theory of the worst she could be up to–"

"Murder or treason. I know the places you'd go for that–more so than normal, anyway," Levi murmured, mind already conjuring the worst areas in the underground, the places where the Underground's worst elements like to stalk the streets, the areas of the highest risk, the worst gangs, the shadiest deals.

The residence search could take months–no one was going to want to talk to a soldier, a surfacer, even someone who had once been a part of the Underground. Not to mention, they had no idea what Y/N Frazier looked like, or what name she was going under while she was hiding in the Underground–if she was, in fact, hiding in the Underground.

Besides, shouldn't he rule out the worst, first?

"I know where to start," Levi said decisively. "It's still going to take some time, though, because she's still aware I'm watching her, and she's good at shaking tales and evasion. Not to mention part of it is going to be based on luck–that I manage to go to the right place at the right time without knowing where she'll be."

"You're good at what you do, Levi. You'll find a way."

So began the unpleasant ritual of Levi going down into the Underground every night of every other week, all in the name of hopefully, eventually, managing to find L/N. All it would take was one glimpse, one time seeing her, and he could follow her, learning from the mistakes of last time to make sure that he didn't lose her this time.

And he could finally find out what was happening below ground–what had been happening for years since she'd suddenly appeared on the surface.

~~~~~~~~~~~~~~~~~~~~~~~~

While Levi had made a name for himself Underground, enough so that it became general knowledge not to test him, he hadn't gone around looking for the kind of trouble that would have brought him to the places he found himself in, now. He'd always been aware of these dark holes in the Underground, and on a few unpleasant occasions had to make a trip to one of them. The worst elements of the Underground were found in these holes–she shadiest deals, the scum of the earth, the darkest corners with the most blood and carnage seeped into and tainting the earth around them.

Levi's every step in these places was careful and quiet, his guard always up, his hood always drawn to hide his face.

Even with the name he'd made down here, he was cautious to use it as a warning sign to keep danger at bay. Not only did he want to avoid sticking out and alerting L/N to his presence if she was down here, but there were always going to be the idiots who wanted to challenge someone who'd made a notorious name for themselves like he had. There might be more than normal who wanted to test him if they knew who he was, people who thought that he was a prime target because his name still stood, but his time above ground might have made him soft.

A terrible, foolish notion, really, since his time above ground and part of the Scouts had only made him more dangerous.

He'd been coming down here regularly since his talk with Erwin, scouting the area and looking for any signs of L/N, whatever they may be. Not many people down here were the talking type, and those who were couldn't give him anything about any surfacer woman prowling the streets. The only thing they could tell him was to not wander these more dangerous parts of the Underground alone because people who did tended to turn up dead or go missing.

That wasn't news to him. He was already well aware of the dangers of these parts of the Underground that had spawned chilling legends even for the people who saw the darkness of the Underground daily. He knew what he was doing was dangerous, which made L/N's presence here all the more questionable if he did manage to see her.

Levi glared fiercely at a man who'd been giving him the target sizing look after glimpsed his clean surfacer clothes. The man slunk back into the shadows and Levi's skin prickled, his senses on high alert for any kind of ambush someone might be tempted to spring on the man leaning against the wall at a four way intersection. He was keeping his head down to keep his face well shielded, but his eyes were constantly flickering around to take in his surroundings, to watch every figure that passed or came down one of the alleys, tense and ready for a fight every time someone came close to him.

This search was slow work, but with no hint to L/N's motivations for being down here besides the scent of blood on her cloak, it was the best option he had.

A familiar, dark robed figure flashed by the opposite end of the alley on his right, and Levi straightened, disbelief flashing through him. Surely that hadn't been...

Before he lost her in his disbelief, Levi moved quickly through the alley to at least get her within his sights, being mindful not to get too close, even though he needed to at least be able to confirm that it was her.

Sticking to the shadows, Levi peered around the corner of the alley, just enough so he could see the cloaked figure and watch them as they continued down the path at a fairly leisurely pace, as if they were strolling along the lakeside instead of through one of the most dangerous parts of the Underground.

He was fairly certain that was her cloak. It was the right color, and a quick glance down revealed that yes, it was long enough to drag along the ground like hers did, but at the moment it was gathered and tucked into the waist to keep it from dragging through the filth, keeping it just above the ankles instead.

And those boots were dark brown, leather, suspiciously similar to the Scout's uniform–even though he couldn't see the rest from this angle, he was willing to bet they went up to the knee. The height was right, the posture seemed militaristic–it was a hard thing to shake, especially when still in active duty and so soon after graduating from the cadets, to boot. Levi held his breath, watching intently and hoping for something a bit more defining that could give him one more bit of evidence to convince him it was her, besides this gut feeling of his.

She took a turn, and while she kept her head down, hood hiding her face, he saw a flash of hair, and glimpsed the civilian clothes underneath–

Civilian clothes he knew were hers because of the day he'd gone through her stuff and saw what she had. She didn't have much, so it was easy to tell this was one of the four pairs she owned.

Not wanting to lose her like he had that first night, Levi hurried forward, keeping his steps as quiet as possible. He had to give her more space then he was used to giving someone that he tailed–he hadn't forgotten how during the expedition, she seemed to have immensely attuned senses, with how quickly and easily she could pick up on what no one else could see. He still didn't want to lose her because he fell too far behind, but he had to be careful–something kept tipping her off to his presence, and while he didn't know what, he had to control everything he could and make it harder for her to notice his presence. Distance was his friend, right now.

It was hard, trying to trail someone while having to put so much distance between them that she frequently turned out of sight, but he kept it up, heart pounding in anticipation as his mental map of the area tried to come up with where she was heading. Right now, it just felt like she was aimlessly wandering, like there was no real direction to where she was going. What the hell was she doing?

After several minutes of following her around like this, Levi started to grow impatient, wondering if she was aware he was following her and was just walking random places until he got bored and left. If anything, it was more likely to make him confront her.

Except he needed to see what she was really doing down here, and if she was aware he was following her, that wasn't going to happen.

Another shadowy figure entered their line, in front of Levi but behind L/N. It was a man, staying far enough back that he clearly wasn't walking with her–another tail. Someone with more sinister intentions, too, Levi would guess, by the way he seemed to be stalking her. With how far back Levi was, he hadn't been noticed by this new party, but he was close enough that Levi was certain L/N had noticed them.

Except...she wasn't trying to shake them. She should have been able to do it with ease after she had lost Levi so easily that first night, but she didn't do anything differently. Her pace remained the same, unhurried and with no real direction, even as the intruder got gradually closer.

What the hell?

Was he wrong? Was it someone she knew that she was meeting up with? No, that looked like something else, Levi knew exactly what this was, he'd seen it enough times to recognize when someone was about to get jumped.

On the other hand...this was perfect for him. Horrible as the initial thought might have been, if he tailed her tail, it put plenty of distance between himself and L/N, and as long as her tail didn't lose her, even with her completely out of sight he wouldn't lose track of her. And if something went wrong, well, he was right here.

Levi shifted his cloak aside at the waist, turning slightly and waiting a few moments before he fired the cables into the nearest building, using it to get onto the roofs and nothing more. The rest could be on foot, no more use of the gear. ODM had a very distinct sound any soldier who had been around them as long as L/N had would recognize instantly, so he didn't dare use it any more times until he'd found what he was looking for. He didn't know how keen those remarkable senses of hers were, if it was her hearing or her sight or hell, even her nose like Miche, that had allowed her to spot those Titans. Because he didn't know how, he couldn't risk it.

Now with the advantage of a higher vantage point, Levi followed L/N's tail from quite a distance, able to see him further and more comfortably from so high up, his footsteps still light and silent even though he was alone on these rooftops.

Being up here reminded him of several things he hadn't fully realized when he'd lived down here, or that he'd learned to ignore or had forgotten in his time above ground. How there was no wind down here, which was disconcerting after so long above ground with fresh air and cool breezes. How dark it really was, even with the orange glow of firelight from homes, impacting his visibility and making it hard to pick out details from a distance. And the stench–he'd been blocking it out, something he'd trained himself to do down here when he wasn't in his own space that he could keep clean, but now that he was higher up and not in the thick of the shit, the air wasn't quite as thick with it.

Slightly. Just barely.

The man he was following sped up and took a sudden turn into a narrow alley, causing Levi to speed up his step as well, keeping an eye on the opposite end of the alley in case he exited the alley before Levi could reach it. Crouched low so that he wouldn't be spotted if someone happened to look up, Levi reached the edge of the building before the alley, his hand placed lightly on the dirt-covered edge as he peered over with care, trying to lean far enough he could see but where he couldn't be seen, or at least would hardly be seen. L/N's tail hadn't left the alley, so they should be–

Before the alley became visible, Levi realized there were no sounds coming from the alley–no sounds of a fight, no drip of blood, no talking, nothing. If her tail had caught up to her, there should have been something coming from the alley below.

A few seconds more, and he had visual confirmation that the alley was empty, even though he hadn't seen anyone leave it from either end.

Levi kept himself calm, not allowing himself to even worry about losing sight of them–he didn't have the time for that. Clearly he'd been far enough behind that he'd missed something that had happened. Maybe they had cut through the building opposite the one he was standing on. There were no sounds coming from there, either–it was silent as the grave in this part of the city, unsettlingly enough. But it let him know they weren't simply hiding in one of the buildings beneath him.

He knew this area–he knew the Underground, had grown up here, walked these streets or at least mapped out in his mind the best and worst places for all kinds of situations. He could figure out what had happened. Whether she got the drop on her tail or her tail had successfully jumped her, if they weren't here they would have gone somewhere discreet, somewhere private that was also nearby. Not a residence, and anything that was dilapidated beyond even entry wouldn't work. What was the best spot for that criteria that was also nearby, close enough it could be quickly ducked into without anyone noticing?

Levi jumped over the edge of the building and dropped back down into the mud, knees bent to absorb the impact before he quickly shifted, navigating the streets quickly and with a purpose as he closed in on the building that came to mind. He was still careful to be quiet and stealthy lest he spook L/N and lose his chance, but he was now running out of time–the longer they were out of sight, the greater the chance he would fail to see what was happening. And he'd come so close, he couldn't let the opportunity slip past him again.

Her being in trouble didn't even cross his mind–he knew she could have shaken that tail if she wanted to, and she had beaten him in a sparring match. Even if that tail jumped her, he doubted she would be the one in trouble.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

*Reader's POV*

The one thing you hated the most about coming to the Underground to hunt was the smell. With how sensitive your senses were, it was absolutely horrid for you. It had taken all of your focus and much of your time when you'd first come down here to learn how to block that foul smell out, though usually it involved handicapping your sense of smell altogether–except for with blood. Blood always pierced through any mental block you'd constructed for yourself.

Still, you were down one sense when you came down here to hunt, refusing to breathe through your nose so you wouldn't become nauseous, sickened by the stench in the air.

The only time that changed down here was when you fed–when the scent of blood filled your every breath with your teeth latched into your most recent kill, warm at first but growing gradually colder as you drained the life from them, a hand over their mouth to muffle any sound or screams until they could make them no more.

Of course you had known about the shady individual tailing you–you had wandered aimlessly in one of the worst parts of the Underground specifically so you could draw someone out, could lure in one of the many victimizers that lurked in these dark corners and turn the tables on them, making their chosen path of victimizing and terror a fatal one. As soon as he entered the dark, isolated alley that you had turned into, you had grabbed him and dashed away with that inhuman speed of yours, pulling him into the nearest abandoned, unowned building where you immediately sank your teeth into him to satiate the hunger that had started to claw at you once again.

Hidden in the darkest corner of the abandoned building, the man had stopped moving beneath you, body turning cold, though from experience you knew he still had more blood to give. You were going to take it all, so it would last you just a little while longer before you had to delve back into the Underground's cesspool for a fresh kill to satiate the hunger again after it returned.

By now, this was normal for you. You had been doing it for decades, and had long worked out your feelings over the moral implications of it all. This was just your way of life, how you survived. And it would continue to be for years and years to come.

One thing about scents down here–there was no wind to carry them away or towards you. So when you picked up on someone's scent, it usually meant they were close...very close. Especially since you went out of your way to block scents down here unless you were in the middle of a feed, like right now.

As such, you stiffened when you caught the beginning traces of a familiar scent, one that was usually carried towards you on a breeze and let you know you were being watched. Tea leaves, cleanliness or cleaning products, hints of mint that might have just been a figment of your own imagination because it was something you associated with a clean smell.

Levi. And if you were catching his scent strongly enough for it to pierce through the blood you were feeding off, then he was dangerously close.

Immediately, you tried to gulp down every last drop you could, wanting to still finish so you wouldn't have to come back down here so soon, even though your instincts were yelling at you to get out of here before he found you. As a result of your suddenly rushed attempts to finish your meal, you made a bit more of a mess than you usually did. Blood smeared across your face and dribbled down onto your shirt, some unfortunately falling to the ground below as your teeth tore into the man's neck in an attempt to get this last bit to gush out.

You could hear him, he was just outside the building, you couldn't wait any longer, you'd already waited too long.

How much had he seen? How long had he been onto you? How had he found you?

You could worry about that when you were safely back at the Scout's headquarters and in the process of cleaning up any evidence you'd ever been to the Underground, right now, you had to leave.

Now you didn't even have time to try and hide the body.

Teeth unlatching from the man's neck, hood pulled low over your head to hide all of your features, you finally bolted, heading for the opposite side as you heard the door open, worried that you still had been too late, that he might have seen your hasty exit, or at least a flash of your cloak disappearing around the corner of the open doorway.

There was no chance to take it back now. The best you could do was damage control and dig in your heels. He might have seen your cloak, maybe, but as far as you knew, he had no way of knowing it was you. No definitive way, anyway. He hadn't seen your face, hadn't seen any defining features. As far as you were aware, he'd only seen your cloak. You still had a chance. Especially if you cleaned your clothes fast enough and thoroughly enough there wasn't a trace of blood or the Underground on them.

Heart pounding as you attempted to keep yourself calm so you could act rationally and not tip your hand and give yourself away by panicking, you raced back to the surface to start disposing of evidence in the safety of your quarters.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

*Levi's POV*

Levi tried to be quick when he opened the door, intending to catch L/N in the middle of whatever was happening in here and then act accordingly. As far as he was aware, he'd acted fast enough and quietly enough he should have gotten the drop on her, even with that apparent sixth sense of hers that had allowed her to avoid him thus far. The door swung open, and he saw a blur of motion–a blur he tried to write off as simply his eyes still adjusting to the scene at first–and the flash of a dark cloak disappearing around the corner.

Levi's eyes widened at the realization that blur or at least the cloak was L/N fleeing from the scene, a 'Tch!' escaping him as he dashed across the abandoned building to try and make it out the other side before she could disappear again, hand on the edge of the doorway as he slid out into the alley on the other side.

Nothing.

He rushed to the mouth, hoping that maybe she had just turned out of sight, that he wasn't about to lose her again like he had the first time he'd followed her.

Again, nothing. Not even the sound of retreating footsteps. She was just...gone, like the first time.

"Shit!"

Swearing loudly to himself, with the sound surprisingly disconcerting when it was thrown out into the silent streets, Levi turned back to the abandoned building, the only thing he had now that L/N had fled.

She had fled, which meant that this time she might have left something behind for him to find in her haste to leave. People got sloppy when they were in a rush, and he was going to take full advantage of it.

Giving one last frustrated look down the deserted street, Levi doubled back to the abandoned building she had been inside, standing in the middle of the room as his eyes did a quick roam over his surroundings, looking for anything out of place, anything out of the ordinary.

Over in a dark corner, there was a mass, some kind of shape that looked distorted and unlike any kind of furniture or item found in an abandoned building like this. It wasn't moving, but Levi still approached with caution, the dark shape slowly taking form as Levi approached, gradually becoming clearer as Levi silently came closer.

It was a body. The tail he'd been following, from the looks of it, though Levi still didn't have a cause of death. The body was distorted and lying unnaturally, head bent at an odd angle–not broken, just left in an odd position–and it was lying face down, as if it had been dropped in a rush.

He had interrupted something. The question now was what had he interrupted. His gaze had already darkened with the realization she'd left a body behind, but whether this had been intentional or self-defense remained to be seen. The motive, her intentions, were largely going to affect how he reacted.

Levi turned the body over with his foot and froze, staring at the man's throat. It was ripped out, like an animal had sunk its teeth all the way in but had been startled into tearing away before it was ready, bringing half the man's throat with it. Yet, despite the gruesome sight, there were only a few drops of blood on the ground beneath the body, a couple light smears around the wound itself. When Levi crouched down to touch the body, it was ice cold against his fingers. Algor mortis shouldn't have even started yet, the man had hardly been dead for a few moments, but there was next to no blood despite his manner of death, the body lacked all warmth–the warmth shouldn't have drained from him for at least a half hour.

There should have been blood all over this place–should have still been some blood in him draining to the parts of his body lying on the ground. And yet...

A memory was making its way unbidden to the front of his mind, whispering sinister, impossible, dark thoughts into his mind as Levi stared at the dead man's throat. A memory of a legend Kenny once tried to scare him with, one he had dismissed as nonsense and scoffed at the impossible tale.

A tale about an immortal creature that plagued the Underground as long as there had been an Underground, choosing the miserable place because of its darkness and isolation from the sun, and its plethora of people that no one would even care if someone went missing every now and then. An undead demon with glowing red eyes, the last thing a man saw before it feasted on his blood and drained the life out of him, leaving his empty body lying in the street with his throat ripped open.

Kenny had told it to him once to scare him, to keep him from getting too cocky and thinking he was untouchable. And Levi had called him out on it, called it the bullshit he'd been so sure that it was. There was no such thing as demons or bloodsucking monsters. There were real monsters in the world, but not of this dark, fantastical variety.

And Kenny had taught him the lesson that had led him here. And made him a bit more wary of the darker corners of the world.

"Maybe not demons...or maybe there are. There's Titans above ground, right? Why wouldn't we have our own brand of monster down here?"

Kenny scratched his chin. "Whether you believe in the demon part or not, there's always a little truth to every legend. At the least, there's probably a killer somewhere down here with a signature like that who caused the stories."

Levi looked dubiously at Kenny. "Yeah? How do I know they're not just legends about your murders."

"Because, Runt. I slit throats, I don't rip 'em out."

Levi felt his blood run cold, chilling him to the core.

What he'd witnessed...she had not been a target, she had never been someone's prey; she had been the hunter luring in an unsuspecting victim.

How long had she been doing this? A couple years at least, going off how long she'd been sneaking out to the Underground, but it probably went on before that, before she joined the military, before she even showed up on the surface. When he'd caught the smell of blood on her cloak he hadn't expected this to be the source.

"I...conduct blood rituals to achieve perfection."

That deadpan delivery at the table in the mess hall–had she been secretly mocking them? Or, more accurately, secretly mocking him, the one trying to figure out what she was hiding?

Was she...even human?

It was insane, but so was the thought of the empty grave before he'd opened that coffin. It was madness, but it fit, it made things that had seemed alien suddenly belong in this greater picture. Where else would all this blood have gone, especially with how quickly she had to leave because of his interruption? How else would she have these senses that told her when Levi was near–that allowed her to know when she was being followed when it should have been impossible, that allowed her to see him in detail in the shadows from a distance yet still draw a perfect portrait, and had made her aware of the Titans before anyone else? That strength and ease in all of her physical requirements as a soldier had to have come from somewhere, like Levi's, but this hadn't been what he was thinking.

And then there was the undead thing, the immortal thing, from the story he'd heard as a child.

No, no that was pushing it too far. That she might not be human was a hard enough pill to swallow, even when he had his own superhuman abilities and lived in a world of Titans. He was not a superstitious person, and this was a hard thought to even entertain, let alone to take seriously. Even when he was staring at a corpse that strongly suggested the truth of the tale.

Even if it would explain how Y/N Frazier crawled out of her grave when it was supposed to be humanly impossible. Even though it smoothed away the question of how Y/N Frazier and Y/N L/N were connected by suggesting they were the same person.

No matter what the full truth was, he was at a point where he had to confront her either way, for everyone's safety. He might be the only one who could match her, physically, and even then he'd have to be extra careful about his approach, because she could still overpower him if he wasn't careful. At the very least, she was a murderer, a serial killer who hadn't stopped even after joining the Scouts and was still regularly killing, and somewhere he used to live, no less. He had hated living down here, but part of him still took that personally.

At the worst, though, she was a monster of shadowy legend. One that preyed on humankind, like the Titans. A true enemy of mankind that it seemed almost no one was aware of. Now he knew, and he had to do something about it.

But first, the confrontation. And he better make sure he had her cornered and that he was ready for a fight. It was likely she would lash out, and he needed to be prepared for a fight for survival. He needed to be ready to handle the situation as soon as he had the truth, because whether she was a murderer or monster only affected how the fight would go and the severity of the stakes. If she was a legitimate monster as well as a murderer did not affect the fact that a fight was inevitable–it just decided how deadly it would actually be.

And he needed a contingency in case the worst happened, so the truth wouldn't die with him.

The Scouts needed to know what lurked within their ranks. Erwin needed to know. It was all a front–something deadly was masquerading as one of them, and it needed to be stopped before it could do irreversible damage.