It started as a meme but there is too much circumstantial evidence to ignore. It seems Shannon, who will be henceforth be called Sayo as she claimed that to be her real name, is not one servant but two.

Leads:

• In 4 episodes they have yet to appear together in a scene where Battler is present. Even when Battler is going around examining every corpse, Kanon is missing.
• We get down to 16 people this way, there's no other way that isn't extremely contrived.
• Being made up characters who don't really exist in reality would give sense and pathos to their struggle to be human in the meta narrative. At least for Kanon.
• Kanon has been working there for only the last three years.
• Kanon has a feminine voice.
• Shannon told George her real name, but Kanon couldn't do the same when asked by Jessica.

Obstacles

• Sometimes you need to steer around some reds to claim they always die and live at the same time.
• Kanon's personal dilemmas at the start of turn are weird under this perspective, but the same scene can also be seen as forshadowing.

Sayo is Kinzo's (not necessarily blood related) granddaughter and daughter of the Beatrice that fell off the cliff 19 years ago. Kinzo wants to hide her identity so he raised her in his orphanage under a different name.

Later he made her take on another identity.

Leads:

• The age fits with the timeframe of Rosa's flashback.
• According to their magical descriptions. Shannon is the first furniture created only by Kinzo, Kanon is the second, better made furniture. The problem with Shannon was that she had a heart.
• Beatrice was raised by Virgilia and she mentions her grandfather in the flashback at the start of Banquet.
• It sounds crazy to suggest that nobody would notice if two servants are never together in the same room for years on end, but it becomes a lot more believable when you add Kinzo pulling the strings. Let's also remember that what servants are at the mention often changes, so they wouldn't have to be together so often.

Sayo is Beatrice in the sense that she is behind most of the murders. We aren't sure to what extent Kinzo's will is involved, but now Sayo is in charge and she aims to convince Battler that magic exists by committing inexplicable crimes.
Therefore, the Beatrice we know if her spiritual equivalent, aka.... her stand.

Leads:

• Someone on Rokkenjima isn't just killing people, they are specifically doing so in ways that will appear magical. Explicitely for the sake of Battler (see the phone calls in Alliance) and maybe for Maria, who at certain points are the only people to be both alive and not in on the plan. This directly parallels the existence of a meta Beatrice fighting Battler in a battle of deduction.
• Sayo is the only known person who could have interacted with Maria in Rokkenjima on repeated occasions to create Mariage Sorcière. For the same reason it's very easy for her to give Maria the letters. She can claim to be Beatrice without needing a disguise.
• "Beatrice mistakes her means for her ends" Maybe the original plan was different, but now she only cares about making it look magical.
• Shannon and Kanon come up over and over as possible culprits. Additionaly, they are some of the select few characters to show knowledge of Rokkenjima time looping in the magical version of the story.
• Endless realization would be a sick stand name.

The other servants plus Nanjo all have motivations to be accomplices of Beatrice.

Leads:

• Genji would do anything related to Kinzo's will. Or alternatively he's following Sayo as his new master after Kinzo died because he sees her, Beatrice, as the true heir.
• Nanjo wants money for his sick grand daughter and Ange shows us that's exactly what his family received.
• Kumasawa's family also got the money, and she has a personal attachment to Sayo.
• Gohda will comply if threatened, he probably isn't even in on the plan from the start.
• This is probably circular evidence, but Ronove Viriglia and Gaap are shown taking orders from Beatrice, implying a relationship of servitude.

This blue truth has been hidden with magic for the purpose of not spoiling future long form theories, please come back later.

Sayo is distinct from X Beatrice, they are two different people.

Leads:

• The Leg Tattoos are too conspicuous of a detail to not be intentional, and they leave no room for doubt.
• Beatrice is not "one individual woman" according to Bernkastel.
• The two of them interact in the meta layer near the end of Alliance in a way that suggests two people with similar goals.