Ryuuma no Gagou

From MangaHelpers: In a world where humanity has turned into prey against the so called "white skin" creatures, one legendary figure known simply as "Ryuma" continues to give hope to this post-apocalyptic society. This individual has many faces and descriptions, but his/her legend has lived continuously in the hearts and minds of the people for half a century. No one knows where this legend started or who started it. Here starts a chronicle to unveil the mysteries of a legend.