Meanwhile Eren, Mikasa and Hange fight the Armored Titan.
Eren had mastered selective-hardening after ingesting the contents of a bottle that said 'Armor' on it. Judging by what you heard from Annie, it was likely the Armored Titan's spinal fluid. You theorize that the Royal Family must've kept a stock of the other titans' spinal fluid since before the defeated king fled to Paradis.
With that, Eren hardens his fists and gets into stance to take Reiner head on. Eren was far better than Reiner at combat after having studied Annie's techniques from afar. Additionally, you and Annie got the chance to teach him a few moves before he left for Karanese after your joint expedition.
Moreover, the Attack titan supposedly has the third best stamina out of the nine titans following the Cart Titan and the Female Titan. It would give Eren the advantage in the event it came down to a test of endurance.
All things considered, Eren should have the edge over the Armored Titan at the moment. However, it would benefit everyone best if he beats the Armored Titan with some stamina left to help out with the Colossal if Armin's plan failed.
Eren wrestles with Reiner and restrains him using an anti-personnel combat technique as Mikasa and Hange dive in from behind and use the recently invented Thunder Spears to break through his armor.
They take him down and cut him out of the nape to take him back alive. You hoped having Annie on your side would help convince him to join you. If he didn't however, the others planned to feed him to someone else and take control of the Armored Titan.
With both his arms and legs cut off, Reiner asks Hange to reach in his pocket and take the letter that Ymir had sent to Historia. Reiner had seemingly lost all hope, but as they were talking, once again the unknown intelligent titan catches them off guard. Zeke throws a smoke bomb and uses the cover to grab Reiner and escape.
Moments before they disappeared behind the smoke, Zeke looks at Eren and says, "Eren Jager... please believe me, I understand what you've been through— we're both victims of that man. I'll definitely come back to save you someday, little brother!"
❋❋❋
Over on your side of the battlefield,
You and Armin confront Bertolt. The Colossal Titan was too powerful of an enemy to fight head on with the forces you had, so Commander Erwin tactfully sent the two best minds next to himself to try and negotiate with Bertolt.
Once the two of you had led him far enough, Armin yells, "Bertolt, we don't want to fight, let's talk this out!"
Bertolt takes a deep breath and responds, "If I talk you you, will you all agree to die?"
"Huh...?" You were confused by the sudden hostility which wasn't like him at all.
"We only want two things; to capture Eren and to annihilate all the humans inside the walls. The decision has already been made, that's the inevitable reality, Armin!" Bertolt explains.
"Who decided that? Marley?" You yell back at him.
Bertolt was taken by surprise as he mustn't have expected you to know about the outside world. He responds, "The fact that you know about Marley and came all the way out here to ambush us could only mean... you already found Eren's basement, didn't you?"
You answer, "We did, and we know how Marley treats Eldians in the internment zone! You're doing this so your family can become Honorary Marleans, aren't you? Listen Bertolt... I want to—"
"I'm impressed... but you're wrong. I'm not just doing this for Marley anymore; I personally want to rid this world of you demons!" He exclaims.
You were utterly shocked by his behavior. It was nothing like the kind and sympathetic Bertolt you felt all that guilt from back in camp; this was a completely different person. As you contemplate on what exactly cause such a polarizing change in such a short period of time, Armin retaliates with some harsh words of his own.
"That's too bad... I was really hoping we wouldn't have to hear any more of Annie's screams." He exclaims.
If it wasn't confusing enough seeing Bertolt's aggressive determination, you weren't expecting such hostility from Armin of all people. You wonder what must have happened after you left as you in turn yell, "Armin, what are you—"
He continues before you could finish, "She's being tortured by the Military Police as we speak because YOU abandoned her. Unless you do something about it, they may as well feed her to the pigs!"
You were pissed at the comments he was making about Annie; just hearing those words in that context made you sick to your stomach. But knowing Armin, he probably had a plan and a premise to believe his comments would affect Bertolt.
Just then, it hits you— it was the same as he did with Annie in Stohess. You figure Bertolt must've had feelings for her and Armin was exploiting them to throw him off. It was an effective strategy indeed; proven by how he managed to back Annie herself into a corner in Stohess.
Considering what it did to her back then, you couldn't stand by and do nothing this time around. You try to intervene, "No Bertolt, Annie's not—"
"Fine by me! Go ahead and feed her to the pigs." Bertolt exclaims. "What? Did you think bringing up Annie's name would get me to break down again?"
It turns out Bertolt didn't need your help as he had seemingly steeled his resolve ahead of time. The way he said 'again' suggested that Armin must've said something similar when they escaped as well and thus Bertolt knew exactly what to expect.
Bertolt continues, "You're not fooling me... I know you're just buying time Armin. You're trying to distract me with idle talk wile Eren and the others kill Reiner, aren't you? Once he does, I'm next, right? Not if I kill you first!"
You quickly grab Armin and retreat seeing Bertolt reaching to bite his finger. At top speed, you barely escape the radius of the blast as Bertolt transforms into the Colossal Titan. Seeing as negotiating was no longer an option, you had no choice but to fight the Colossal Titan.
The forest would've given you an advantage, as it was the ideal environment for ODM gear. The gigantic trees were taller than the Colossal Titan, making it easier to reach its nape. However, the explosion from his transformation took out the trees and leveled a considerable area, taking away the only advantage you had.
As the titan slowly made its way towards you, Armin apologizes for the remarks he made about Annie and comes up with a rather desperate plan to fight the Colossal. He gives you his remaining blades and asks, "Can you throw these at his nape? I saw you kill a titan like that on the way here."
"I did but... that was kind of a fluke, you know. I'm not sure if I'll be able to pull it off again." You explain.
Armin responds, "We have no other choice! I'm going to distract him. I want you to go around back and aim for his nape."
"B-but if I fail, you'll..." as you express your concern, Armin says, "I'm prepared for it. If you don't want that to happen, then take him out before that!"
It was one of Levi's moves which you tried to emulate. When he cleaned your ODM gear following your joint mission, you noticed how he had lubricated the release mechanism— which wasn't something you're usually supposed to do. You figure he must've done it out of habit and reverse the logic to figure out that it was the key to his technique.
It involved releasing the blade from the handle at just the right moment to send it spinning towards a target at a medium range. The blades were thin and substantially more aerodynamic than Thunder Spears, so they would make it through the steam if thrown at exactly the right angle.
Even though you weren't confident in it at all, you had no choice as Armin wasn't willing to change his mind. You drench your Survey Corps cloak in a nearby stream and wrap it around Armin to hopefully reduce the damage from the heat.
Once you did, Armin dives into the jets of scalding steam to distract the Colossal Titan as you go in from behind and attempt to throw your blades at the nape. You miss the first few times as expected. But seeing how you were running out of blades and Armin was reaching his limit, you make a last ditch effort.
The blade makes it through the steam and strikes the nape, slicing its way into Bertolt's chest. It didn't kill him, but it disturbed him enough to stop the steam for just a second when you and Armin quickly dive in and cut him out of the nape.