Speaking with Famitsu, Tabata said HexaDrive was working with them since before Final Fantasy XV was integrated with the Luminous Engine—when the development environment was still running on its former Ebony Engine. In terms of timing, cooperation began a little before the game’s E3 2013 re-debut.
During the Final Fantasy Versus XIII days, the development team set their sights high as they went about developing it the same ways they had other Final Fantasy and Kingdom Hearts games, but things never quite came together and it was stuck in an experimentation phase. This experience made the team vividly aware that with the existing structure, they wouldn’t be able to actually put out a high-definition game of such a massive scale, so the development structure and content of the game itself was thoroughly re-evaluated.
With re-evaluation came a new work flow and structure that came to include people from Square Enix’s Technology Promotion team and Visual Works division, with HexaDrive providing additional technical support, all of which formed the basis of the current development structure.
The results of the new development environment, as well as HexaDrive’s support, was showcased in the E3 2013 trailer.
Tabata also mentions that both Square Enix and HexaDrive staff went location scouting for caves in Chiba prefecture to create the dungeon playable in the Final Fantasy XV: Episode Duscae demo.
HexaDrive isn’t the only external developer working on Final Fantasy XV. At the Taipei Game Show in February, Square Enix revealed Taiwanese company XPEC Entertainment is one of many outside firms also lending a hand in development.