Theories TLDR

Here's a quick list of concepts from the episodes 1 and 2 theories that are still relevant. Some of them may be altered or outright contradicted if they conflict with more up to date insight.

Legend

• Kanon and Shannon are the same person. We call her Sayo, and she is also Beatrice, aka. the main culprit of the murders.
• Crafting an occult narrative behind the murders is her top priority (endless witch).
• There's no gold, just the illusion of it (golden witch).
• Sayo's accomplices on the island include at least Genji, Kumasawa, and Nanjo. She also has some financial and logistical backing from outside, including captain Kawabata and possibly the Ushiromiya group.
• On the day of the family conference, sometime before the first twilight, Eva and Hideyoshi are also convinced to lend a hand.
• Sayo ends up faking her death twice (first as Shannon, then as Kanon), then she betrays her accomplices when it's the only way of fulfilling the pattern.
• Some automatic and highly destructive mechanism kills every survivor still in the mansion at midnight of the second day. We imagine it could be a set of very powerful explosives.
• Kinzo is alway dead from the start in every episode. Natsuhi and Krauss are doing their best to hide this fact from the others.
• The Ushiromiya Eva that returns in the future may not be the real Eva.
• In the meta layer of the tea party where magic exists, Beato is playing a game against Bernkastel, and by extension us, the reader.

Turn

• The Beatrice we see appear in front of the characters (X Beatrice) is another person distinct from Sayo, but they're close and tend to work together in our theories, except when they don't.
• X Beatrice may or may not be able to convincingly pull off a Shannon disguise.
• The narrator is on the witch side, and when given the chance they will twist a scene until it barely resembles what really happened.
• If no reliable witnesses are alive after an event, that event usually gets retold as an over the top magical scene.
• Sayo is struggling with being in a relationship with George and developing feelings for Jessica at the same time.
• You can interpret the scenes where Kanon and Shannon defend Jessica and George as Sayo feeling conflicted and either changing her mind and being murdered as Kanon or discarding those personas and continuing on with her witch ways.
• This time Rosa is the improvised accomplice instead of Eva, her cooperation is paramount to explaining several of the mysteries.
• Battler being emotionally forced to submit and accept magic will not count as a victory for the witch side.
• Beatrice deliberately goes easy on Battler.