According to Yushihiro Kitao, Star Ocean and Beyond the Labyrinth developer tri-Ace assisted Square Enix with Final Fantasy XIII-2.
According to Siliconera's translation of Kitao's tweet, tri-Ace's involvement extended beyond outsourcing a few assets, with the independent developer lending a hand on game design, art and programming.
Industry sleuth Miladesn noted that the game's credits suggest some development was outsourced to a third, Chinese company.
In addition to those mentioned above, RPG specialist Tri-Ace's works include Infinite Undiscovery, resonance of Fate, Valkyrie Profile, and the upcoming Frontier Gate. Several of the company's games have been published by Square Enix.
Final Fantasy XIII-2 released in Japan last week, and arrives in the West on PlayStation 3 and Xbox 360 in early 2012.