Short answer: No. Toboso Yana is the creator and writer of the Twisted Wonderland main story.
There is a credits page in the Twst app listing Yana’s various roles which was removed from the EN game, contributing to this misunderstanding.
Long answer: Yana posted in April of 2024 that all the scenarios of the main story are handled by Yana herself.
Not “Yana and her company” or any reference to any other assistants, but literally “All scenarios in the main story are handled by Toboso.”
Every time new content is released in Twst Yana responds with a comment explaining her role in the project. For example, taking full credit for every installment of Twisted Wonderland’s main story, including Book 6 and Book 7. ( source 1 ▶︎ / source 2 ▶︎ )
But if Yana is the creator of the main story, then where did this Book 6 rumor come from?
It is possibly from a post Yana made in August 2021 where she thanked both the Japan- and US-Disney branches for their support. Yana did not give credit to US-Disney for the creation of the arc.
Yana did not say “EN Disney took over Book 6,” she thanked colleagues for the investment of their time in helping make sure the the delicate subject matter that she herself wrote for Book 6 was handled appropriately.
It seems there were a few people misunderstood what she meant, however, because Yana herself then had to address it:
“Main Story Chapter 6 “Guardian of the Underworld”I was in charge of the scenario and character design.
In depicting this chapter, which is deeply connected to the ‘Land of the Dead,’ I received tremendous support from everyone at WDJ and the US headquarters. I express my deepest gratitude. I hope you enjoy it!
It seems that the way it was written caused some misunderstandings, so let me clarify.
From the prologue to Chapter 5, we have received supervision and assistance from everyone at WDJ and the US headquarters. The process of scenario completion → English translation → supervision → revision is always followed without exception, so it’s not just about Chapter 6.
This time, since we are touching on the extremely sensitive concept of “death,” which is inseparable from “The Land of the Dead,” we decided to proceed with greater caution, seeking supervision and advice, and thus taking up the time of everyone at the related companies…that was the meaning. I apologize for the tweet that lacked sufficient explanation.“
IIt is possible that some people maybe saw Yana’s first tweet only, realized she had never mentioned receiving this support in any other of her tweets, and decided that there was some special meaning when it was just Yana being polite.
It would be interesting to see what proof is being spread alongside claims that Disney-US was involved any more than usual in Book 6, just in case there is a chance that something is being misunderstood, but as of this writing such proof has yet to surface.
For more information on Yana’s role in Twisted Wonderland, please see her official interviews: Toboso Yana (2020 Interview) (Magical Archives Game Guide) / Toboso Yana (2023 Interview) (Apple Store)
Twisted Wonderland Reference Note 