Summary
The first flashback is Traumerei weeping over his shinheuh, who got mass murdered some people. Gustang tells him to stop crying, and how it won't bring them back. Traumerei says he wants to hunt down all the people who murdered his shinheuh, because his shinheuh were their companions and they didn't do anything wrong to deserve it. Gustang tells him how the Tower is vast and if they killed them, eventually they would end up lonely. Traumerei says how it's fine, and he only needs "Us" to be here and not feel lonely and everything else can be burnt down, and how he wants to disconnect himself from the "wretched Tower". How he needs to be strong, endlessly strong.
The next flashback is Zahard talking to Traumerei, telling him not to hesitate. How the first time Traumerei pulled the lever(likely related to their experiments), Traumerei felt helplessness and crushing guilt with a guilty conscience, and told Traumerei that they shouldn't have emotions like that, and they are the absolute line and should not feel guilty
The next part is essentially Traumerei saying how he won't feel lonely, even if Gustang is gone now. Gustang "died" on purpose, and has a contract that summons a Scale of Judgement(made by the Workshop's Great Teacher) that can view people's past with his writing in blood. The problem is that Traumerei is a transcendental being, according to the scale, and his past can't be viewed normally, so Gustang had to exchange his life to view Traumerei's past sins. If it turns out that Traumerei is a murderer/sinner without guilt and does not repent, then Gustang will come back as an "Absolute Executor"(As in one who executes an action)
We then see a flashback of the past, where the FHs first interacted with the mechanical kingdom. They are all running from the robots, and Traumerei and Gustang meet up with Yirang underground. Yirang is chased by robots, Traumerei asks if they should wait for V and Zahard, since the shinsoo density in the area is very high, but they end up jumping into some pool/warp thing, and end up further underground. They see a GoG look alike, and the area is a power source that can depower the mechs, but there's also a rice pot lookalike and the GoG lookalike asks them to wait, since someone is inside. V comes out and he was there for about 10 minutes, They are all like "V?"(Also apparently whatever he did in there destroyed his clothes, thats why he is only in briefs)