"Even at a late stage of development, we did not agree on key elements of the game, which stemmed from the lack of a cohesive vision, the lack of finalized specs, and the remaining problems with communication between departments.
What enabled us to conquer this line of seemingly endless conflicts was the development process for the Final Fantasy XIII demo, which was included in the Japan-only Blu-ray version of the animated film Final Fantasy VII: Advent Children Complete. The demo was not in our original plan, so we had to make adjustments to the overall schedule to accommodate it. Whatever effects creating the demo had on the schedule, once it was complete we realized it was just the panacea we needed.
With a tangible version of the game that could actually be played, internal debates transitioned from theoretical discussions based solely on abstract concepts to concrete dialogue. The demo not only unified the vision and understanding of the games direction across the entire development team, but it was also the first time that everyone could see exactly how the assets they worked on would function within the game. During the internal postmortem, many team members noted that the demo was what finally allowed them to truly realize and embrace the vision for Final Fantasy XIII.
Although a vertical slice is commonplace in Western development, this was never actually practiced with our teams unless there was a company requirement. In retrospect, the demo acted as our vertical slice, and its effectiveness was felt full force by each and every member of the team. This was an essential key learning point that affected how we approached game development moving forward."