Finally, I recovered from the shock this episode delivered to me, because I was fully in angst all this episode, and a the next batch of fresh revelations made both uncomfortable and queasy. But, perhaps, Eren's nonchalant or take-it-easy attitude as he received the despairing news became too much for me to seriously stomach.
I'm telling you the next half of the show is going to get sour, distressing, and unpleasant to go through.
Spoiler:
So, after all the tensed reactions and suspicious behaviour, what Berthold and Reiner got around between themselves kept secret is that they were the Colossal and Armored Titans who wreak their chaos on humanity five years ago with their destruction of Wall Maria.
I don't know what to make of Reiner's bipolar reactions, because I'm more messed up than Berthold was when Reiner spilled the beans to Eren so non-chalantly.
But, anyways, this hasn't been the first time something of this insane magnitude has manifested in Attack on Titan. The episode discussed on a flashback the contents of the parchment that Sasha brought to Hange, and Annie's case may serve as a grim remainder from Erwin urging Eren not to be deceived what the eyes see way back to season one.
Reiner, Berthold, Annie, and their were of the same bunch of buddies coming from the same place supposedly to wipe out all of humanity inside the walls. The chaos that ensued after fall of Wall Maria allowed them to cover their tracks and infiltrate the cadet corps. However, the deception was eventually found due to the intel on Annie revealing sharing the same origins with her two comrades.
So, exactly, what begs the question is it for Berthold and Reiner to utterly massacre humanity as their commited mission? and why address themselves as warriors?}
Answers, likely, will have to wait, because the ensuing horror has to be dealt with in the next episode now that Eren starts to go apeshit on his former fellows. But, perhaps, what's more distressing and crying in anguish is Eren sorting out the past memories of his friends-turned-to-foes about the times they spent their times together as cadets against the grim reality that has abruptly changed.
Back in the previous season, Mikasa ominously warned Eren that the world is cruel and relentless, and if he wants to survive then he must not hesitate to ready his hands bathing in blood, if so be it. That hotheadedness and indecision cost him severely two times previously against Annie, a.k.a. Female titan. And, if he spares just a tiny speck of doubt on Reiner and Berthold, then I cannot fathom a dark future for Eren but either getting captured or devoured by those two traitors.