This newer saga in the Final Fantasy series has garnered a lot of attention. The original FF XIII game itself has been criticized for being linear, and the inclusion of a trilogy has never been done in any other FF. It is interesting to see how Square-Enix is working around with the story and continuing the Fabula Nova Crystallis timeline.
As such there are many artists on Pixiv who have been submitting their own work for years. I went through putting together this huge showcase of digital artwork + illustrations related to Final Fantasy XIII and XIII-2.