Once you have the inspiration, it is time for the perspiration.
Embodying the idea seems to work well as a single action, with the result being compared to the difficulty of the creation. Now, I want revision to be a normal part of creation, so the first result should generally not be high enough to succeed. The easiest thing to do here is to just take the total of the first roll, and use that as the progress towards creation.
The next step is assessment, looking at what has been achieved so far. This is best done by someone other than the person who embodied the idea; it is a truism of creation that you cannot effectively assess your own work. Of course, it is not impossible to do this for your own work, just difficult, and progressively harder the more revisions you have looked at. This is probably best reflected in a penalty to the number of dice to roll, and this penalty should go up every time you try to assess your own work. Other personae get no penalty the first time, but after that they start to take the penalty, because they are also getting too close to the work.
The difficulty of the assessment should be based on the current progress towards the difficulty of the creation, so that it gets harder to see places for improvement as the work gets nearer to completion. However, it seems likely that the assessment and embodying totals will be about the same, so the difficulty should not be the same as the current progress. It should be possible to make progress even though none of the personae stand a chance of completing the work in one roll. A simple rule would be to double the result of the assessment roll, and compare that to the progress. If this total exceeds the progress, the assessment has succeeded, providing useful insight into the creation.
A successful assessment creates the option to revise the work. The revision roll may use the same total as initial creation, or, in some cases, might be different. To get the difficulty for the revision roll, subtract the current progress of the creation from the total on the assessment roll, after doubling. This is always a positive number for a successful assessment, because the assessment total exceeded the progress of the creation. Then subtract this result, the amount by which the assessment total exceeded the progress, from the progress, to get the difficulty of the revision. If the work has not made much progress, improvement is quite easy, and if the assessment is very successful it is also easy. The difficulty of the revision cannot drop below zero; if the assessment total was more than twice the current progress, the revision difficulty is zero.
After the revision roll, increase the progress of the creation by the amount by which the revision roll exceeded the revision difficulty.
So, for example, suppose that Yoshihiko rolls 6 and keeps 3 (R6K3) for his embodying roll. He gets 13. Aya rolls 5 and keeps 2 for her assessment. She rolls an 11, doubled to 22. That’s 9 greater than the progress on the work, so the difficulty for Yoshihiko’s next embodying roll is 13–9, which is 4. He rolls 11, which means that he can add 11–4, or 7, to the progress, for a total of 20. At this point, Aya and Yoshihiko are probably stuck, because Aya only gets to roll four dice to assess the work a second time, so her chances of getting over 20 are slim; she would need to get 11 or 12 on the two dice she keeps. They need to find someone else, ideally someone who keeps at least three dice for assessment, to make further progress.
A revision need not increase the progress. Instead, a revision may add another concept to the creation. In this case, the assessment roll is followed by a conception roll, rather than an embodying roll. The difficulty of the revision is subtracted from the points available to set the benefits and difficulty of the new concept, which will typically make this harder than just having a new idea. In addition, the difficulty of the new concept is added to the existing difficulty of the creation. Not only does the revision not increase progress, it actually pushes completion further away. It is hard to incorporate too many ideas into the same creation, but extra ideas do make the final product better.
This pattern allows several personae to contribute to a creation, but it doesn’t give the players many choices, and it doesn’t describe the creation. That is where elements come in.