In the future where half of Alliance takes place, accounts of at least the first three games have been recovered inside different bottles in the sea near Rokkenjima.
The legend letter has been signed with Maria's name, but it's not her handwriting, it's the handwriting of the person who Maria knew as Beatrice. Ange was able to know this because of a passage she wrote in Maria's diary.
Hilariously, when compared to Higurashi the game Beatrice plays against Bernkaster is almost literally 4D chess. You have multiple chessboards stacked on top of each other and then you have pieces like Ange moving along the time axis.
Theories
The Beatrice who wrote the letters is either Sayo or X Beatrice but not both, she is the same person who wrote in Maria's diary, and knowing who she is would help us decide is meta Beato represents only Sayo or all of them.
Rokkenjima is in a superposition because of the letters
Nobody really knows what happened there, all we have are the Bottled letters all giving a different account of the events, and the four episodes we see are four of such letters, out of an unknown amount.
From a magical point of view, it's this uncertainty that allows the entire island to cycle through endless possibilities and be regularly populated by witches and demons. A perfect schrodinger's box.
Leads:
- Beatrice "never lets the dice fall" according to Bernkastel. You never get to see the result so she can keep feeding you different versions of the same story. A true nightmare for someone who systematically rules out wrong approaches like Bern.
- Bernkastel's letter#Rule Y : Beatrice has opened up a world in a way none of the other witches expected.
The future Ange lives in is the only future and it follows from the real course of events, all the different episodes are just different stories passed down as Bottled letters.
Ok, but then what ACTUALLY happened on Rokkenjima in reality?
Two theories:
Legend is the "canonical" version of the events.
We were asked on more than one occasion which episode we expected to be the "real" one.
We don't know how many if any more games will happen in the answer arcs, but if we're choosing from the question arcs there are some arguments for Legend being the one. Although there's also a big obstacle.
Leads:
- The first tea party is a direct continuation of Legend, and every following interaction between Battler and Beatrice is framed as a continuation of that one. A discrepancy in the character description colors further supports this reading.
- Beatrice, Shannon and Kanon claim to have seen countless loops already, but this is merely the same magic fluff as the witch killing and reviving someone 100 times.
Obstacles:
- Directly contradicted by the credits of legend saying that nobody was found alive, not even Eva.
The "canonical" version of the events will be the one where Battler wins the game.
We just haven't seen it yet, because the mystery hasn't been solved.
Leads:
- If the truth about what transpired on Rokkenjima were to be revealed, that means Battler will have won and the black box will be broken.
- The framing of the Bottled letters would suggest that Legend is yet another letter, but who says that any of them recount the real story?