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.

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

Claim...

Leads:

Obstacles:

• optional

It was X beato, not Sayo, who had a coping mechanism that Battler destroyed.

Leads:

• The sin is not between him and Beatrice, who we associate with Sayo.
• She is the one talking to Battler in reality during that scene. She has the outfit and at that point Sayo is probably dead, (although we're not 100% on that).
• In the meta layer she is the one with regrets about the sin, and she looks hurt after he doesn't remember.
• Crunter said so and that's the best answer we got.

The supposed corpse of Shannon isn't hers and it also isn't a corpse. That is simply X Beatrice trying to hide herself with the help of the adults.

Leads:

• We can beat the red by simply claiming that the person there wasn't dead and thus not an unidentified corpse.
• Maybe after seeing the girl from the portrait show up the Ushiromiya parents want to keep it a secret in fear for the inheritance.
• There's room for a 17th person in Legend.

Obstacles:

• Does the motive make any sense with the whole murder going on? Would this be the priority of a bunch of greedy but otherwise innocent people? And are the kids really the ones to whom this secret needs to be kept?
• Her presence isn't required for any Legend solution, and her being here would break an interesting pattern with the episodes.