Thinking about my zexal characters in 5ds au and the crimson dragon really made some Choices regarding who should be a signer
Both Shark and Rio are Signers. Thomas is too, and he is so fed up with all of this/hates being forced to work with the Kamishiros for any reason. (The Kamishiros in turn don't like Thomas much either.)
Kaito is also there, and he has arguably the best knowledge of what the goal is here since his father is functionally our stand in for both Rex and Rutger Godwin and actually shared info with his son, but it's also Kaito so good luck getting him to work with his squabbling teammates.
They still haven't found the fifth Signer, btw. Nor do any of them realize Dr. Faker caused Zero Reverse/killed Thomas' dad Byron.
(Byron, meanwhile, has been hanging around on Satellite as a Dark Signer for the past ten years. A solid decade of Earthbound God induced madness and anger directed at Dr. Faker was not good for him.)