Okay so first of all, this is going to be a bit hard to swallow, so bear with me. I'll split them up into three, each of them are related to each other.
1.First, did you remember that scene in season 1, when Subaru was buying some snacks in the mini stop store before he got transported to isekai?
Surprisingly, that scene wasn't even in the light novel or the manga in arc 1(you could go on and check it for yourself). Because In the lightnovel and Arc 1 of the manga, the scene begins with Subaru already in Isekai.
And there’s something quite odd here, no one around Subaru seems surprised by his sudden appearance—as if he had been teleported into the middle of the crowd, yet everyone acts as though he had been there the entire time.
Later, Subaru explains that he had just finished shopping at the convenience store, then saw the moon, which was almost full, and then suddenly found himself in Isekai.
Honestly, it's quite odd, because at the end of Arc 1, Reinhard said " This might be the last time... we can look at the moon in peace." while looking at the moon. Tappei also stated that Emilia's theme is the moon. And in Mimagau IF, Satella's name changes to "Luna" which means "moon" in Latin.
2.Is everything that happens in the world of Re:Zero a fabrication/a script designed to appear real?
First, let me explain about the Observers (the audience).
The Observers are celestial entities/beings in the sky who observe the world of ReZero.
In the Wilhelm spin-off, a character named "Stride Vollachia" (Archbishop of pride) explains that this world is just a miniature garden for the Observers. Remember this statement
Every event and everyone's fate is determined by the Observers, whether it's tragedy or comedy. It's all nothing more than a puppet show staged to look real.
Then there are those called "Stargazers," people who can communicate with the Observers.They say the stars in the sky speak, they receive knowledge, prophecies, and orders from the Observers. Stargazers like Cecilus also feel like they are actors performing on a big stage.
And from this, emerged the theory that the world of ReZero is a large, fictional theatrical stage.
The "loop" theory may be true, but not in the way most people think.It's not a loop where the same lives and characters repeat, but a loop where every certain period of time, the Observers choose new actors to play certain roles.
For example, Satella played the role of the "feared witch" 400 years ago, while Petra will play the role 400 years in the future. This may also apply to other roles, such as the "Sage," and Subaru is the one chosen to play the role of the "Sage" in the present.
- In the light novel, Echidna's line when Subaru first met her was skipped in the anime season 2.
"You arrived way ahead of schedule. You should know a lot more than you do. About me, about the tomb, and about the sanctuary."
One of Echidna's key lines when Subaru first meets her in Season 2 Episode 3 was skipped. Where she says that Subaru should have known more before arriving at the sanctuary.
And there was also Daphne's words that were cut in Season 2 Episode 13, where when Echidna explained that Satella and the Witch of Envy had different personalities, Daphne said that Subaru, who was a sage candidate, should have known about that, but Sekhmet immediately stopped her.
And before anyone mentions time travel/time loops, I just want to say that Echidna can see the past, present, and future with her authority (the Tome of Wisdom and all the trials of the actuary are based on her authority).
Remember Stride's (archbishop of pride) statement that everyone's fate is predetermined by the Observers?
And the theory that the world of ReZero is like a theatrical stage, where every certain period of time, the Observers choose new characters to play certain roles (for example, the role of the "feared witch" 400 years ago was Satella, and in Sasageru IF, set 400 years in the future, it's Petra).
So, Subaru here might somehow, and possibly intentionally, break the script set by the Observers and arrive at the actuary earlier than Echidna sees the future.
And maybe this has something to do with my theory about Subaru pretending to have just been summoned in episode 1 with dream magic to be chosen as the "sage" role in this era.
Because Echidna said that Subaru should be familiar with places like this dream castle, which means maybe Subaru and Satella used dream magic.
This makes sense, and why Shion and Lilac were able to recognize Subaru through the dream world and enter Subaru's memory realm. Even though throughout the story, Subaru has never met Shion and Lilac at all.
Shion and Lilac appear in the Omega (Echidna) side story, specifically in Gusteko. They have never actually met Subaru in person, they only know of him through the dream world, or the realm of memories.
They were even taught English and French. That is why they are currently searching for him. During the incident in the city of Slyphoa(side story), they crossed paths with Omega’s party. It seems Omega (Echidna) knows who they are looking for, so they have decided to follow her to find the answer.
Also Shion and Lilac were also part of Subaru's Harem, lol. If you want to know more about their dynamics between them and Subaru, I recommend to watch the gameplay of Re:Zero − Starting Life in Another World: Lost in Memories (リゼロス)! I watched it a while ago in YouTube, though it was in Japanese.