In the cruel word, humanity was granted one mercy -- a promise, that somewhere out there, there is someone just for you, and the single hint to search for them by. A coordinate, where that person could be found.

But that single blessing could become a curse.

Finding their one -- their other half, their soulmate -- could be almost a fairytale. A dream as impossible as traveling beyond the Walls.

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Some had a mark. Some had a song. Those were the most common.

Carla had a song. It was an irony in itself -- Grisha had never sung, never so much as hummed. There was no lilt to his voice, no hint to what he might sound like. Still, Carla was a skilled singer. She knew voices. She had insisted. She had been certain. He was hers.

But when he quietly, almost furtively stumbled his way through a lullaby for Eren, she had cried in relief.

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Eren was Carla's child, in so many ways, but not in this.

He loved songs and singing. He learned gladly every song Carla knew and looked for more. He sang often and freely.

But what Eren had wasn't a song. It wasn't even a dream, like his father. It was a mark. On his back was a pair of wings, one black, one white.

It reminded Carla of the crest of the madmen who passed through their town on their way beyond, outside the Walls. The once who so often returned with grievous wounds of the body and mind, or didn't return at all.

She feared for Eren, for the day that mark would fade away as surely as the life of the person it led to. She also feared for Eren, that he might go seeking the one bearing those wings.

"Don't show it to anyone," Carla told him. "It's something between just the two of you."

Ever rebellious, Eren looked at her dubiously, but this time he listened. "What does it look like?" he wondered, trying to crane his head far enough to see his own back.

"I'll tell you when you're older," Carla promised. She didn't know what to feel about the knowledge that by the time Eren asked again, there might be no mark to explain to him.

---------------

Eren took her words to heart. He never asked after the marks of others, whether they were dreams or songs or tattoos, or something else altogether.

He didn't ask Armin, who wouldn't have told him even if he had. Armin never told anyone.

The Church taught that the coordinates were a blessing from God, given to His chosen people within the Walls. Armin had said, just once, that the Church was wrong. He'd meant that they had existed long before people came to live within the Walls, but the local bullies had decided he meant that he had no coordinate, nothing to guide him to his one.

Or maybe, that he had no one to be guided to. No soulmate. No one who wanted him.

Maybe, he had no soul at all... It had escalated from there, to the worst beating Armin had ever received. He was lucky it didn't turn into a lynching, the way it still happened in most remote villages.

They were wrong. But their words had hurt, more than they knew.

After that, Armin stubbornly refused to reveal the form of his coordinate -- or who it led to.

He also never explained why he only let Eren drag him to see the Survey Corps once and refused to go ever again.

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The Church called it a blessing from God, but Mikasa's mother had her own stories for how the coordinates came to be, passed down in her family.

They had their own shape as well -- a red thread, tying them to their one.

Mikasa's mother had held up her pinky, a smile on her lips as her eyes followed the unseen string to where Mikasa's father was, just outside the window. Mikasa had glanced down at her own hand and her own thread.

It was slack, dropping to the floor and trailing away through the wall and into the forest beyond. Mikasa never thought much of it, in all the time she and her family lived peacefully in their little house in the mountains.

It wasn't until she came to live with Eren, in Zhiganshina, that Mikasa realized something.

The thread always led south. South, south, south, even when she and Eren stood at the southern edge of town, right before the Wall itself.

Eren hadn't understood the meaning of her gesture -- staring at one hand, only the smallest finger extended -- or the expression on her face as she glanced up at the Wall.

That was the only time she agreed with him -- she wanted to go outside too.

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Were there people on the other side of the Walls? Did they have souls as well? Were they searching for their soulmates too?

(Yes. Yes. Yes.)

---------------

He used to have two marks, one for each of his friends -- balanced, symmetrical, perfect.

Now, there was only one. One mark, one friend -- one soulmate.

He would never forget the nightmarish vision of the Titan's gaping maw as it devoured the other that should have been with them.

He didn't think about the many nightmares he would figure in, after this.

---------------

How many marks faded away the day Maria fell?

How many in the days after?

How many in the year to follow?

The scope of the tragedy was beyond anyone's understanding. It resonated through the people, regardless of birthplace or status. Sometimes, one's soulmate could be found on the other side of a Wall. Sometimes, there was no way of knowing until they were gone.

When Maria fell, how many woke up crying as bond after bond was broken?

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There were a small handful born without a coordinate. It was always a carefully guarded secret, and revealing it had led to mobs and witch hunts in ages past. Lacking something so fundamental was seen as an indication of some greater defect, as a sign of something inhuman.

So Erwin had carefully kept his own lack of mark, or song, or dream, hidden from everyone, including his closest friends and even his family.

It had been surprisingly easy. Sometimes, the coordinate did not appear for a few years, and by the point where it would have become suspicious, Erwin was already able to lie convincingly enough. No one saw it as terribly strange that he was quite secretive about something he had been so anxiously waiting for, as they saw it.

In fact, it didn't appear by his tenth birthday, or his twentieth. By then, he had already given up.

What did it mean, anyway, to have someone meant for you and to be meant for someone in return? It wasn't a guarantee of happiness. Was he really missing something so vital? He certainly didn't feel that way. You couldn't miss what you never had.

(Except when he did. Sometimes, at the very edge of sleep, he would feel a soul-deep longing that had not yet been given a shape.)

Erwin realized how wrong he had been the day the coordinate finally appeared. He had been missing something all along, even if he had never understood what it was.

He remembered that day as surely as his own birthday, because that's what it was -- the day his soulmate was born.

Erwin was so overjoyed it took some time for the full reality of the situation to sink it. He had wanted to search for them, now that he finally could, but was that really the right choice? Who would he find? An infant?

No, it wouldn't be right at all. Meant for each other or not, they were separate people with their own lives to live. That child deserved a chance to live their own life, to stand on their own two feet, without Erwin's overshadowing, smothering presence.

Because Erwin knew that once he found them, he would cling and never let go.

Instead, he waited. He had already waited for so long, after all.

He fought with more determination than ever before.

He counted the years.

---------------

It might have seemed strange, that Erwin remained alone for so long and had been alone his entire adult life, but in the Survey Corps, asking about soulmates and coordinates was almost taboo. There were too many whose marks and dreams and songs had faded away into nothing, all too often before their promise had been fulfilled.

Those that had their one... the others did their best to dissuade them. Only a fool would throw away not only their own life, but that one person meant for you. What would they feel like, having their own coordinate fade into nothing, without warning or explanation?

Those few that could still keep hoping were allowed certain leeway. Like Mike, and his drive to sample the smell of every person he came across in search of that one scent he knew better than his own.

---------------

Scowling viciously, Levi made a point of fixing his uniform after Mike finally let him be.

"Oh well, I guess you're not the one," Hange sighed, shrugging lightheartedly. "Too bad."

"The one?" Levi muttered.

"You know, his one. His soulmate," she explained absently. "Everyone knows Mike's looking for them by their scent."

Even Levi's pokerface didn't quite hide his blank lack of understanding, though Hange misunderstood the subtle shift in his expression. She smiled sympathetically and didn't ask, assuming the worst.

---------------

That wasn't the first time Levi had heard of soulmates, of course, but it had always been in passing, overhearing secretive whispers that seemed too outlandish and whimsical to be true.

He had never been willing to show weakness by asking, and no one had ever told him. So everything about coordinates remained a mystery to him.

That was the reason why Levi had never realized what the song in his heart really meant. It had begun one day, when it seemed like Levi had hit rock bottom. He had almost thought it was a sign of his mind finally unhinging. If that was the case, insanity was already far more pleasant than sanity had ever been.

He didn't realize what it meant when the song grew louder after he left Sina.

It wasn't until his first expedition beyond the Walls that Levi gave himself away. He couldn't stop himself from turning to look back as the song faded sharply, the further they traveled from the gates.

When they returned, their group now so much smaller, the others tried to tease him about being scared to travel beyond the Walls and the way he relaxed after returning. Levi ignored them, but as the survivors' "celebration" -- really drinking themselves into a stupor in grief and relief -- continued, he found himself growing more and more agitated.

"You've got that look on your face," Hange noted, sidling up to him and ignoring his glare.

"What look?" Levi snapped.

Her smile was strange as she said, "The 'thinking about your soulmate' look. I can tell. That's why you looked back when we were leaving, and why you reacted like that about Mike, right?"

She was quick to it figure out, and something about the way she looked at him made Levi hesitate to brush her off again. It was probably the alcohol, and the memory of the Titans' grotesque faces, swallowing his comrades, but Levi found himself suddenly speaking.

He was trusting Hange and the others with his life. What did it matter, if he revealed this too?

"There's a song," Levi began, trying to find the words. "I've been hearing it for a long time..."

-------------

Hange listened to him calmly and seriously. She didn't laugh or joke or look like she thought he was insane.

Then she explained.

"Are you going to look for them?" she asked, in the end. "The Commander would probably be willing to give you some time off, for this."

For several moments, Levi hesitated. Finally, he shook his head.

"Huh? Why not?" Hange wondered. She looked almost stricken, unable to understand why he would say that.

Levi shrugged, turning away. "I don't believe in fairytales," he said.

It was true, he didn't believe in happy endings. He didn't believe he would find any happiness, in the end.

He had already dedicated all of himself to a cause. There was no room for meaningless dreams.

---------------

After Wall Maria fell -- after his mother was eaten before his eyes -- Eren couldn't himself to sing again. What was there to sing for? There was no happiness in their cruel world.

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Notes:

Coordinate 1. A number representing the position of a point along a line, arc, or similar one-dimensional figure. 2. Something that is equal to another thing. (I am ~so subtle.)