Notes:
This is my first reibert fic ever. I hope you like my characterization. This is how I imagine Bertl went through witnessing Reiner's mental issues and how he felt about integrating with the others.
Initially, Bertholdt had tried to understand why Reiner seemed to put so much time and efforts into playing the friendly, paternal big brother to the rest of the kids in the trainee division. He had always preferred to stay in Reiner's shadow, content with remaining in a quiet, observing stance. At first, he saw it as some kind of mastermind plan his partner must have had. Keep your friends close, and your enemies closer, right?
He had thought that it was cold…Maybe downright evil. (Not that it shocked him, it was not worse than anything they had already done. Just a mere observation, if you will.)
Reiner was manipulating the strings behind the scene, playing their comrades, putting them exactly where they needed to be. Good, that would save him the trouble of having to interact with them too much. He did not want to get involved. He did not want to -feel- for them, as much as Bertholdt could feel, that is. He knew Reiner was not getting emotionally invested either. Reiner was strong, he knew what they had to do. He was the leader between the two of them. They would both look forward, putting the mission above all else; the mission was everything.
As the weeks and the months passed, his cold exterior remained, it always did. It was not a taxing effort, it just came naturally to him. He would quietly stand in the background, towering over everybody else around him. From time to time, he would comment on something someone had said with a quiet voice. Reactions differed depending on who he was talking to. The group sometimes turned to him, almost surprised he had spoken. Other times, his words went by as if he had not opened his mouth at all, and nobody even bothered to turn around to try to include him in the conversation.
He did not mind; this was just a little less of a burden on his shoulders, after all. He had expected that it would take a lot of focus and constant efforts to go unnoticed, him, the Colossal Titan, the mass murderer in disguise who hid behind the face of a rather plain-looking man. Since he had obtained the power of Titan Shifting, he had always felt like he was a monster pretending to be a human, and not the other way around.
He had been apprehensive at first. Afraid, even. Of course, he would not have used that word; that was not something he expressed out loud, even to his partner; his friend, his confident, the only person that mattered in this twisted existence of his. However, yes, he had attempted to express this feeling as he had calmly discussed with Reiner. He had told him about how hard fitting in with the others might be once they would join the training corp, and how hiding their true identity and purpose might be difficult.
Reiner had encouraged him, wrapping one of his large, muscular arms around Bertholdt's slimmer shoulders. "That's okay. We'll do what we have to do. We're warriors."
"Yeah, we're warriors." Bertholdt had replied.
In truth, months later, a lost-in-thought Bertholdt recalled this memory and realized that no, it had not actually been difficult at all. Everyone had trusted them from day one. To their fellow trainees, him and Reiner were comrades, friends, confidants. Well, especially Reiner. The accuracy with which he played this role would sometimes make Bertholdt…Well. It made a slight upward curl appear on the corner of his lips. It was too subtle to really be called a smile.
It had been a year since they had begun training when Bertholdt realized the "flawless realism" behind Reiner's actions might have not been caused entirely by some sort of excellent manipulative skills he happened to possess. Training was harsh and arduous, even for Reiner and Bertholdt's sharp minds and already well-trained bodies. There was only 1 day off a week, and half of it was dedicated to cleaning and maintenance. On their afternoon off, they would often leave the compound and go talk in a nearby thicket, after making sure absolutely nobody had followed them. This is where they would regroup and discuss the plan, the mission, or their feelings about it all. There was no way they could risk discussing it on the training grounds, even in the middle of the night.
"I think I'm going to join the Scouting Legion, Bertl." Reiner had said as they sat against a tree, a hopeful, determined sparkle in his brown eyes.
"Well…yes, that's been the plan all along, right?" He had replied softly, a neutral tone to his quiet voice.
Yes, that was the plan, once they would complete training, they would join the Scouting Legion. The front lines were the best place to be to keep a track on humanity's progress, to sabotage it, and to work on the advancement of their own goals.
Reiner looked up to the sky through the tree leaves that towered above them. "I think there is hope…I think we can really do it, defeat the Titans."
Bertholdt had raised an eyebrow in confusion, turning his attention to his friend's face. "What are you saying Reiner? We're alone now, you don't have to…"
The tall, blonde-haired man continued: "I think humanity really stands a chance. I haven't lost faith, we're going to avenge everyone else's death Bertl, you understand? That Jaeger kid, he really motivated me, man. I'm not afraid to die anymore.
Bertholdt's expression became more and more confused with every sentences Reiner uttered. "R-Reiner…? What are you saying?" He repeated, as he could already feel nervous sweats running down his back and causing his shirt to stick to his skin uncomfortably.
"We're not going to save humanity…It's rotten, it doesn't deserve to be saved…Isn't that what you think too…I-isn't that what you said?"
He asked as he stared at his knees, with a slightly sad expression on his face. Something lit up in Reiner's eyes suddenly.
"Yeah, of course, I don't know what I was thinking." Bertholdt barely spoke for the rest of the day, lost in thought even more than usual, trying to understand why Reiner had acted this way, and failing to do so.
Even though Bertholdt still had no interest in forming relationships with the other trainees, after a year or two, it had happened. Others had begun reaching out to him first. Connie, Jean, Eren, Armin, Marco…They all talked to him, they included him in their conversations. They'd turn to the quiet giant and ask "Isn't that right, Bertl?" and "What do you think Bertl?" They'd tell him, laughing, about the odd positions he had contorted into in the middle of the night without even realizing.
Why are they even watching me sleep?
They'd ask about his plans for the future, if he wanted to have children, get married, what branch he would join.
Why do they care? Why? Why does it even matter to them?
Even though he did nothing for the others to notice him, it had happened. Even though he would have been fine with nobody saying his name or even looking in his direction for 3 years, save for Reiner "please Reiner, never stop," he almost felt a certain envy at the others for "being people," as he called it. Everyone had an essence to them. Eren was the boy with the unlimited resolve, Armin was intelligent, Mikasa was strong, Jean was honest, Marco was kind…
Even Reiner's persona had found its niche. He was the big guy taking care of everyone. The real Reiner had goals too: He wanted the mission to be a success and had done everything in his power for it to happen. He would push Bertholdt and encourage him, and tell him that this was their destiny. "We are warriors!" He would shout.
Him? He was nobody, he was nothing. He was a mass murderer, a monster in a human shell, who did not know what he was doing, or why, or if he even cared to know. He did not know why he was alive, or why he existed, or why it mattered at all. Why even go on? He looked over at Reiner who was playing around with Connie and Jean, inwardly knowing the exact reason why.
Every time Reiner would have his "episodes", as Bertholdt now called them, he felt like whatever parts of his heart he still had left was being crushed. If Reiner stopped caring about the mission, then he would most definitely stop caring about him. Reiner was his pillar, the reason he went on, the reason he had even given up his soul and humanity in the first place.
If Reiner was going to forget it all and leave him alone with the burden of their acts, then it would be all over. Bertholdt could not imagine an existence without him. He knew with absolute certitude that he would end it, the only question was would be whether he would rampage in his Colossal Titan form within the walls until he had been killed, or they all had, or if he would simply die a little less of a monster by stabbing himself in the back of the neck somewhere in some nameless forest. He had not made his choice yet, and he still had enough hope left to wish it would not end this way.
After the episodes had happened a few times, Bertholdt had realized that the easiest way to trigger Reiner back was to say: "Hey Reiner, you're not a soldier, you're a warrior." And just like that, he would snap out of his dissociative state and return to his normal self without mentioning it. Bertholdt would never bring it up, he would just carry on the conversation they had had before Reiner snapped, or they would not talk at all. He almost felt guilty for taking his partner out of the bliss his brain had created for itself, but it had to be done. For the mission, for me.
He knew he was being selfish, but he had already done so much for Reiner. He had thrown his humanity away, and now Reiner was just going to leave him behind? That just was not fair. It was not going to be like this. Was this what resentment felt like?
A year and then two passed again, and now, the "keyword" did not always work anymore. Bertl would just sit and listen to Reiner's delusions, nodding helplessly through them, feeling his heart break each time.
"I can't believe it's almost time for graduation already. We did it Bertl, we came so far…You're going to join the Scouting Legion with me, right?"
"Yes, Reiner…"
Reiner was losing his grip on reality, and Reiner was Berthold's reality. Was it a mistake all along? The plan, the mission, breaching the wall.
One night, while all the recruits under suspicion were kept unarmed and ungeared at a facility, Reiner asked Bert if he could talk to him outside. They were not allowed to leave, but they had managed to sneak out for a moment into some nearby empty field.
"I think they know."
"There's no way they can know, we're okay."
"No, no, I see it, in their eyes. The way they look at me. They know Bertl, they know I'm the armored titan, they know we killed everyone."
"Reiner, it's in your head…"
"I'm going to tell them, I'm going to tell Eren and…I'm going to tell him, he's gonna come with us. We won't have to hurt anyone anymore."
Bertl felt his heartbeat speed up and the cold sweats all the way down his neck again. He knew Reiner wasn't joking. He never joked anymore.
"Reiner, you can't. Not now, not after everything we've been through. You CAN'T!" He had raised his voice a little more than his normal tone of voice. It was barely louder than Reiner's usual pitch, though.
"I can't live with this anymore."
"YOU can't?!" Bertholdt could not believe what he was going to say. They had never acknowledged this before. He did not know why, he just did not want to bring it up. He would now.
"YOU CAN'T?! You've been dissociating for half of it! What do you think it's like for me!? What do you think it feels like watching you forget who you are, who we are?! I have nobody else but you, and you're letting go…The mission Reiner, you can't…give up on the mission. You can't give up on…"
Me. He did not finish his sentence, letting his voice trail off.
Reiner's face contorted into a pained expression. He looked down and nodded in defeat. "You're right…I'm sorry Bertholdt. I won't."
A few days later, during the aftermath of the attack at Castle Utgard, Bertholdt stood completely helpless as he watched Reiner finally break down.
"Eren, I need to talk to you…5 years ago…We destroyed the wall and launched the attack on humanity. I'm the Armored Titan." He had rested his hand on Bertholdt's shaking shoulder. "And he's the Collosal Type Titan."
Right then, at that very moment, Bertholdt knew it was the beginning of the end.