TL;DR
If the Pleiades Watchtower is merely a facility for watching Satella, it is absurdly overbuilt. It contains trials, the Great Library, Books of the Dead, the Corridor of Memories, Reid, Volcanica, and Shaula. GitHub Actions did not exist four hundred years ago, so perhaps Flugel had to build his handoff server out of an actual tower.
The main theory is this:
Future Subaru = Flugel failed to solve a problem four hundred years ago. He therefore left failure logs, memories, authentication, and permissions in Pleiades so that the Subaru of four hundred years later — a Subaru who has not yet become Flugel — can try again.
Add future Emilia = Satella, and Satella’s unexplained reason for taking an incompatible Witch Factor gains a possible motive: she did it to save Subaru. The rescue attempt broke her because she was incompatible with the Factor, producing the Envy personality and the catastrophe.
Flugel is then trapped in a causal chicken-and-egg problem: save himself and Emilia breaks; save Emilia and the chain that saves/creates his side may fail. Instead of handing his younger self an answer, he may have handed him a record of how he failed.
This is not canon. The annoying part is that the more canon pieces we add, the more often the response becomes: “Yes, the setting can absolutely do that.”
1. Canon first: the tower is not merely a “watchtower”
[Canon] Shaula explains that the place’s original role is the Great Library Pleiades. The upper-floor trials are also treated by Subaru as something like clearance tests for access to information.
So the facility already performs several jobs:
- stores information;
- tests entrants;
- grants access only after conditions are met;
- stores lives as Books of the Dead;
- connects to the mysterious Corridor of Memories;
- houses Reid, Volcanica, and Shaula.
That is not a security camera. That is a data center, archive, boss rush, and identity service sharing one building.
2. The Earth-star puzzle is terrible as a public exam, excellent as authentication
[Canon] One trial pushes Subaru through Shaula the star, Scorpius, the Orion myth, the layout of Orion, and finally Rigel. Subaru himself notices that very few people in this world could even possess the knowledge needed to answer it.
As an exam for “the best people in the fantasy world,” this is defective. Do not test fantasy residents on Earth astronomy and mythology.
As a check for “the person who shares my Earth knowledge and is supposed to arrive centuries later,” however, it is excellent.
Pleiades, Shaula, and the floor names turn the tower into a giant password manager. Unfair to locals; strong two-factor authentication for a successor.
3. Flugel is suspiciously Subaru-shaped
[Canon] Flugel has Earth-linked knowledge. His name survived partly because someone carved the equivalent of “Flugel was here” high on the great tree. Subaru mocks it as school-trip graffiti and immediately admits that he himself felt a similar urge.
[Canon] In Arc 10 Subaru again notes that Flügel means “wing” in German, and the story reminds us that Subaru once had a phase of searching for cool German words.
[Canon] Shaula recognizes Subaru as her master not from his face but from his abnormally intense Witch-related smell.
“Another Earth person” can explain some of this. Future Subaru himself explains more with fewer extra assumptions:
- Earth knowledge: because he is Subaru;
- similar naming taste: Subaru;
- “was here” behavior: Subaru;
- Shaula’s recognition: the same person or same underlying signature;
- no memories of four hundred years ago: because for young Subaru, those events have not happened yet.
That last point is especially elegant. A reincarnation theory needs memory erasure. A future-to-past theory does not.
4. Add Satella = future Emilia, and the pattern becomes uncomfortably neat
[Canon] Satella and Emilia are extraordinarily alike. Volcanica, who knew Satella four hundred years ago, calls Emilia “Satella” and speaks to her as though addressing someone familiar. At the top of the tower, Emilia also sees a handprint that seems like her own.
[Canon] Satella gives very specific reasons for loving Subaru: he brought her light, showed her the outside world, held her hand through lonely nights, and kissed her when she was alone.
Those details echo Subaru and Emilia’s relationship far too well to ignore as theory fuel.
[Theory] If a future Emilia travels to four hundred years ago and lives as Satella, then Satella can possess the “later chapters” of a romance that young Subaru has not experienced yet.
Young Subaru: “Who are you?”
Future Emilia/Satella: “I have already read to the end.”
Classic time-travel asymmetry, now with elf ears.
5. Central hypothesis: Satella broke because she tried to save Subaru
This is the core of the theory.
[Canon] Satella took a Witch Factor for which she lacked compatibility, and this produced a separate Witch-like personality corresponding to Envy. However, canon does not let us dump every historical atrocity onto “the evil second personality”; Satella herself remains tied to the catastrophe. The distinction must be handled carefully.
[Canon] Subaru’s miasma grows denser as Return by Death is repeated.
What is not canon is “the Witch Factor itself levels up every death.” So the safer version is:
[Theory] Repeated Return by Death makes Subaru increasingly entangled with Witch Factors, Satella, miasma, and the world’s time rules. Eventually future Subaru reaches a state he cannot resolve alone.
Future Emilia/Satella then chooses:
“You kept saving me. This time I will save you.”
She takes the dangerous core — a Factor, Authority, or central mechanism — from him or for him.
She is incompatible.
The rescue turns into personality fracture, runaway power, and the ancient disaster.
Structurally, it resembles Homura accumulating causality around Madoka, followed by Madoka reaching into the rules of the world to save everyone. In Re:ZERO terms, it is less “Soul Gem gets dark” and more “unsupported operating system; user clicked Force Install anyway.”
6. Now we have a giant chicken-and-egg loop
Suppose the four-hundred-year disaster also participates in establishing Return by Death.
Young Subaru returns by death
→ repeats it until his connection becomes abnormal
→ future Subaru goes four hundred years back
→ Satella takes the dangerous core to save him
→ the Witch of Envy problem is born
→ that event helps establish young Subaru’s Return by Death
→ back to the start.
Where is the first cause?
There may not be one. It exists inside the circle.
That is a bootstrap paradox / causal loop. It is the horror of finding a save file under your own name dated earlier than your game installation.
7. Why Flugel cannot solve it: he is part of the bug
If the loop is real, future Subaru/Flugel faces a terrible binary.
A: Save himself
→ Emilia/Satella takes the dangerous burden to save him and breaks.
B: Save Emilia
→ the chain that saves Subaru, creates Return by Death, or sustains the established history fails.
The person solving the problem is also one of the variables. Hundreds of retries with the same memories, love, and assumptions may simply return him to the same local minimum.
So Flugel’s escape is not “try harder.” It is:
“I cannot solve this anymore. Let the version of me who does not know my conclusion solve it.”
Young Subaru is not causally blank. But he is psychologically blank with respect to Flugel’s final failure. The same person can be raised by different experiences.
8. Pleiades as a 400-year handoff server
Now the tower’s excess hardware suddenly has jobs:
- star puzzle → successor authentication;
- trials → access control;
- Great Library → long-term storage;
- Books of the Dead → life/death logs;
- Corridor of Memories → deep-memory interface;
- Reid, Volcanica, Shaula → defense, verification, and witnesses from four hundred years ago.
[Canon] There are multiple Books of the Dead for “Natsuki Subaru,” corresponding even to deaths that should have vanished with Return by Death. Subaru explicitly notes that such records require his deaths to have been observed from outside the apparent reset, and Flugel is named as a likely controller behind the system.
[Theory] Pleiades may not be a machine that travels through time. It may be a machine that lets information survive time rewrites.
In other words:
save data + strategy wiki + identity authentication + permissions + a handoff document addressed four hundred years into the future.
An isekai backup server.
9. Arc 6 amnesia may be a rehearsal for the final mechanism
This is one of the strongest structural reasons to like the theory.
Arc 6 already performs a miniature version:
- Subaru loses his old memories.
- A “new” Subaru gains experiences without knowing the old Subaru.
- He reads Books of the Dead belonging to Natsuki Subaru.
- He learns his former self from an outside perspective.
- Old and new selves are integrated, and he moves forward.
[Theory] Scale that up to the whole series:
- Flugel fails four hundred years ago.
- He stores his failure logs in Pleiades.
- Young Subaru grows without knowing Flugel’s conclusion.
- Emilia, Rem, Beatrice, Otto, Garfiel, and others shape him into a version who may think differently from Flugel.
- Once mature enough, he loads Flugel’s information/memories.
- “I understand why you failed. But I will choose my own answer.”
Arc 6 would then be a small-scale demonstration of the final series architecture.
10. Re:ZERO keeps rejecting A-or-B and manufacturing a third answer
Subaru’s growth is repeatedly about refusing imposed sacrifice binaries. He does not become great by choosing A instead of B more efficiently. He increasingly tries to say: “Stop forcing this binary. I will make a route where both survive.”
So if the final problem is:
save Subaru / save Emilia
the answer is likely neither.
Save both. If necessary, break the causal structure that created the binary.
Present Subaru creates option C, the answer that old Flugel could not find.
If the endpoint of Subaru’s growth is not “become better at dying” but “learn to build solutions with other people that Return by Death alone cannot produce,” that would fit Re:ZERO extremely well.
11. Why it feels like Steins;Gate, Madoka Magica, and ONE PIECE
These are structural analogies, not evidence.
Steins;Gate
A failed future does not send back a perfect answer; it sends back failure information. Future knowledge is valuable because it says what did not work.
Madoka Magica
The rescuer loops repeatedly, causality accumulates, and eventually the person being rescued reaches into the world’s rules to save the rescuer. A Re:ZERO version could also reverse who is saving whom midway through the loop.
ONE PIECE
“Everything happened four hundred years ago.”
→ Fine, explain four hundred years ago.
→ There was a mysterious man named Flugel.
→ Then explain that guy.
Do not enter a tower to solve one mystery and leave carrying a larger mystery.
12. If this theory is right, the endgame may look like this
A deliberately aggressive prediction:
Subaru’s group reaches the core of the Satella problem
→ the cause cannot be cut from the present alone
→ connection to the events of four hundred years ago becomes necessary
→ Subaru and Emilia become participants in that era
→ Subaru becomes/uses the name Flugel; Emilia becomes/uses the name Satella
→ Satella takes the Factor/Authority core to save Subaru
→ incompatibility causes collapse
→ Flugel fails to achieve a complete solution
→ Satella is sealed; Pleiades is prepared as a handoff
→ young Subaru begins from episode one and eventually reaches the tower
→ he receives the failure data
→ at the final confrontation, he chooses the third answer Flugel could not.
If Subaru eventually announces that he has to go four hundred years into the past, many readers may simply say:
“Ah. Yes. We are finally doing that.”
Time travel itself is no longer the surprise. The surprise must be what happened there and why a four-century self-handoff became necessary.
13. Weak points: what could kill this theory
A serious theory needs failure conditions.
- Flugel = future Subaru is not confirmed. Another Earth person, shared soul, copy, or other mechanism could explain part of the evidence.
- Satella = future Emilia is not confirmed. Blood relation or another form of identity link could explain resemblance and misrecognition.
- “Satella took the Witch Factor to save Subaru” is pure theory. Canon gives the incompatible absorption and its consequence, not the motive.
- Repeated Return by Death is confirmed to increase miasma; amplification of the Witch Factor itself is not established.
- Pleiades has not been confirmed to contain a full memory backup of Flugel.
- In a perfectly fixed single timeline, Flugel’s attempt to delegate the decision may itself be part of the fixed loop. The story would still need a mechanism that permits a genuinely new option C.
The pieces are numerous. The central gear is still deliberately hidden.
14. Subjective probability table
| Theory | Subjective probability | Why |
|---|---|---|
| The tower also exists to hand off information/roles | 85% | clearance trials + library + Dead Books |
| Flugel and Subaru have direct identity continuity | 90% | Earth knowledge, naming, personality gags, Shaula recognition |
| Flugel = future Subaru | 70% | elegantly explains missing memories |
| Satella and Emilia have direct identity continuity | 75% | appearance, Volcanica, handprint, love memories |
| Satella = future Emilia | 65% | time loop handles simultaneous existence |
| Satella took the dangerous core to save Subaru | 50% | excellent missing motive, no direct proof |
| Arc 6 self-integration foreshadows loading Flugel’s memories | 70% | same narrative mechanism already demonstrated |
| Final answer rejects “Subaru or Emilia” and creates a third option | 80% | strongly matches the series’ problem-solving pattern |
These numbers are not evidence percentages. They mean: how efficiently does the hypothesis connect the known pieces without inventing extra machinery?
Conclusion — the tower may be a gigantic handoff note from Subaru’s own past/future self
Arc 6 initially makes Pleiades look like the place where the four-hundred-year mystery will finally be solved. Instead, clearing it adds the even larger mystery of Flugel.
That can be frustrating — unless that is the point.
Perhaps Flugel did not store the answer. He stored the problem he could not solve, the ways he failed, and the material his next self would need.
Four hundred years later, Natsuki Subaru arrives before he has been contaminated by Flugel’s conclusion.
The tower may be asking only one real question:
“I got stuck here four hundred years ago. You have now read everything. What will you do?”
If Subaru’s response is not to choose whom to sacrifice but to destroy the binary itself, that would be the largest possible version of what Return by Death has trained him to do all along.
Then Re:ZERO was never merely an isekai fantasy with a retry ability. It was a four-hundred-year causal-loop SF story about handing your own failed save file to a different version of yourself.
And honestly, that would finally make the “please stop adding more 400-year mysteries” complaint pay off.
Primary novel checkpoints
- Arc 4-76: https://ncode.syosetu.com/n2267be/243/
- Arc 4-78: https://ncode.syosetu.com/n2267be/245/
- Arc 6-20: https://ncode.syosetu.com/n2267be/422/
- Arc 6-22: https://ncode.syosetu.com/n2267be/424/
- Arc 6-74: https://ncode.syosetu.com/n2267be/480/
- Arc 6-87: https://ncode.syosetu.com/n2267be/494/
- Arc 7-9: https://ncode.syosetu.com/n2267be/506/
- Arc 9-11: https://ncode.syosetu.com/n2267be/706/
- Arc 10-31: https://ncode.syosetu.com/n2267be/791/
- Arc 10-35: https://ncode.syosetu.com/n2267be/795/
