Everyone keeps repeating the same things in different amounts, so here's the full dealio;
"The Suikoden series is loosely based on a classical Chinese novel, Shui Hu Zhuan (Outlaws of the Marsh), by Shi Nai'an and Luo Guanzhong."
http://en.wikipedia.org/wiki/Shui_Hu_Zhuan for more details on said Chinese novel.
The anime "Suikoden: Demon Century" is not a movie, but a full series of anime that was not released in America. Only the first part was released in America, so they only got up to like 5 stars of destiny. It has nothing to do with Genso Suikoden, and was merely based on Shui Hu Zhuan.
How many threads can we have talking about the same topic..?