Samurai Deeper Kyo revolves mainly around the character of Onime no Kyo (Demon Eyes Kyo, named for his red eyes), a man who is legendary for killing a thousand men. He was sealed inside the body of the medicine-seller Kyoshiro Mibu after the battle of Sekigahara. Throughout the anime series, he and his companions must fight creatures called "Kenyou", humans who became like demons after the battle. Both manga and anime incorporate real historical figures, though they have a much greater role in the manga. The anime follows the vague plot of the manga until volume sixteen, though it then dissolves into a completely ridiculous ending. It also ignores most of the character development of some of the most interesting people, and cuts out others completely. The manga is 38 volumes long, there are no Kenyou, it's much more amusing and it has infinitely better fight scenes. My suggestion: READ Samurai Deeper Kyo. You will find yourself much happier than if you only watch the anime.