Otto sums up the whole situation in Arc 4 pretty nicely
[Otto : So, you're telling me the Great Rabbit will come here soon, and we must depend on Emilia-sama to pass the Trial to escape with everyone, which seems little bit difficult for her. If we try to escape with villagers not affected by the barrier, we will be interrupted by a bastard. If we finally return to the mansion, we will be assassinated by the hit-man sent from the owner of the mansion. What the hell is this situation!?]
Nevertheless, gaining support from Otto and Ram (Ram's reason will be explained in later synopsis), Subaru first defeats Garfiel, which continues into this conversation between Emilia and Roswaal.
After defeating Garfiel, Ram and Subaru both persuade him into their side. Subaru, Garfiel, and Otto together go to the mansion for the rescue, leaving Ram and Emilia in Sanctuary.
Subaru orders Otto to rescue Petra (Who had 100% fatality rate in every loops according to him), Garfiel to face Elsa, and he himself goes to persuade Beatrice.
Entering Forbidden Archive, Beatrice first doubts Subaru's intention to bring her out when whole mansion is in chaos. When Beatrice tells Subaru she's safe in here, Subaru reveals Elsa already knows how to break its defense, which brings suspicion from her.
[Beatrice : How that woman knows the countermeasure to Betty's Door Crossing? No one could imagine that seeing Betty's Door Crossing for the first time. It must be the person who knows Betty well.]
[Subaru : Beatrice, there's no time for...]
[Beatrice : It's Roswaal. Then, Roswaal's Gospel might have ordered him to kill Betty, I suppose.]
Beatrice is relieved on that she was mentioned in Roswaal's Gospel, and Subaru tries to persuade her out. Their discussion goes into Beatrice comparing her meaningless life to her gospel, which is all blank for 400 years. Subaru continues conversation comparing her to book onward, then notices it was his mistake to continue comparing her to the book, when she isn't in reality.
[Beatrice : If I was a simple heartless book, I could have believed in my mother's order without any doubt. Staying as lovable Beatrice to mother. ]
[Beatrice : However, Betty has heart. With enough time spent to start doubting what I wanted to believe, I remember many things. Worrying that I can't remember mother's face, gathering every fragments of memory on some nights!]
[Beatrice : There were times when I can't stand being alone and wants to interact with someone. However, they all leave Betty alone anyway! Saying they have something more important or whatever, abandoning Betty with incomprehensible reasons! Mother! Roswaal! Lewes!]
(Losing her strength)
[Beatrice : So, it's okay now. Betty's Gospel doesn't write Betty's future. I already knew Betty's fate is abandoned by mother from the start. If Roswaal's Gospel showed Bety's fate, it's really cruel, but also relieving. Roswaal must have done something suitable.]
[Subaru : Even when you're about to be killed by acquaintance, why...]
[Beatrice : Of course, If at least Roswaal's Gospel showed Betty's fate, that means mother never forgot Betty completely.]
Hearing that, Subaru also snaps.
[Subaru : Accepting your fate? You're same as Roswaal. No, even worse than him, who at least knows what he's doing. You're a fool. Fate, mother's order or whatever, it's pitiful to see you from side. Having heart? Not same as a book? It's obvious, you bastard. You can't even know that when stuck in this stinky room?]
(Beatrice stands up furiously)
[Beatrice : You! You know who you're talking to! Fool, fool? Magnificently said!What do you know about Betty, I suppose!?]
[Subaru : I know you better than you because I know you're a fool, when you don't even know it yourself! You fool! Baka! Baka! Baka!!]
[Subaru : 400 years of blank? Stop being proud of that! You've been just grabbing your knees for 400 years! With that much time to think, why are you still clinging to only one answer? You want to tell me because the book didn't told you anything, you were trying hard not to do anything? Fool!]
[Beatrice : Of course, I tried thinking, I suppose! Betty tried indefinite time to see if the Gospel changes! However, no matter what I did or waited, it never changed! So!]
[Subaru : That's exactly what I'm telling you you're a fool! "I couldn't write anything on a book, so I tried hard to make it write on its own?" Nobody writes that even on a New Year's card nowadays! If you tried that hard but nothing happens, think it in other way!]
Beatrice doesn't believe her mother's order was like what Subaru is telling her.
[Subaru : Then, I will talk clearly, to make fools like you and your mother (Echidna) understand. Stop being dragged around by the blank book and a promise made 400 years ago. Choose what you want to do on your own, Beatrice.]
Beatrice becomes furious on Subaru and casts her magic to send him flying into the wall.
[Beatrice : Contract is absolute! It was a promise between a Witch and a spirit. You're telling me to terminate it from side of the spirit? You don't know anything, I suppose! That's unforgivable to anyone, anybody, even from Betty!]
[Subaru : It's funny to hear that from the person who found the back door, trying to kill herself when unable to break the contract]
They continue their talk about the promise, until Beatrice reaches one crucial question, which Echidna wanted to see the result of.
[Beatrice : If you're... 'That Person'... Would you become... 'That Person' for Betty?]
[Subaru : Are you stupid? Of course, I'm not your 'That Person' who nobody knows of.]
Hearing that, Beatrice immediately uses her magic to kick Subaru out from her library.
After Subaru is kicked out from Forbidden Archive, he meets everyone (Frederica carrying Rem, Petra, Otto, Garfiel) gathered in the mansion, and soon they are surrounded by Elsa and various mabeasts, controlled by the disappeared girl (Meili) he saw in Arc 2
[Meili : It's that Oni-chan! Even Petra-chan is here, long time no see!]
[Subaru : You're talking like normal. Don't you understand this situation?]
[Meili : I know and I'm working~. I will be scolded by mama if I don't do this right. By the way, Elsa is really acting as she pleases.]
[Elsa : Being the reserve is boring. It's wrong to put me on that position in the first place. It would be better to be killed by me than being eaten by the beasts. Your choice?]
[Subaru : Good. Then, I will give you the coolest proposal ever. Turn your knife, stab your own stomach, and move it either way. You and I are both happy from seeing your own guts. It's hara-kiri challenge. How's that?]
[Meili : Ahahahahahaha! That's splendid! Elsa, let's try it! Elsa, you really like guts. It must be funny!]
[Elsa : Unfortunately, when I became like this, I already tried and bored from doing it.]
Anyway, Subaru and his co leave Garfiel to face Elsa and all the mabeasts (Which he does) and run away, noticing 'the reserve' means Elsa was originally ordered to guard the secret passage, and it is now empty with Elsa's independent act.
However, Meili already left a large mabeast there to fill the gap, which is defeated by the fire from Otto's oil mentioned in Arc 3
(Before using oil, Subaru tries to show off his modern knowledge by using dust explosion to defeat it, only to fail and scolded by Otto for doing senseless thing.)
Fire soon spreads all over the mansion, and Subaru sends others into secret passage to escape, while he goes back into the mansion to find Beatrice.
Petra even doubt Beatrice's existence because she never saw her, but Subaru asks her to be a friend with Beatrice after everything is over, which leads to this conversation.
[Subaru : Petra, if I come back with Beatrice, you should become a friend with her. Petra might like her, because it's really worthwhile to tease her.]
[Petra : More than Otto-san?]
[Subaru : Yes. Even Otto will become useless compared to her. As I told, I will find Beatrice. I will try my best not to be burnt to death. But if I does, make it clear that the cause of death was Otto's oil.]
Continues onto Part 5
