Once on flickr I took part in a debate (argument?) about Natura. Some people said it was a unique film, I suspected it was re-branded Superia 1600.
Someone wrote to Fuji and got a reply saying that it was indeed Superia 1600 and that it was re-branded to match the Natura camera range.
Another member said that they were different films because his US-based Fuji rep had told him so.
I downloaded the datasheets for Superia 1600 and Natura 1600, the latter was in Japanese, but I was able to compare tables, graphs and numbers. What I found was that judged by the datasheets, Superia 1600 and Natura 1600 are identical.