Lord Himuro Gemma
Himuro Gemma is Jubei's arch nemesis, and has been even before being leader of the Devils of Kimon. It turns out that Gemma had betrayed Jubei and tricked Jubei's own clan into trying to kill him for being a traitor. In turn Jubei was forced to kill the Yamashiro clan in self defense, and then avenge their deaths by sending Gemma to hell.
Gemma has the ability to re-generate his body parts, including his once severed head. Because of this power, Gemma's arrogance tells us that he thinks he is a god. Gemma is totally ruthless and wants Jubei to suffer. To regenerate takes total concentration and control of one's body, and Gemma has perfected it to an art form, so much so that he can also take sifferent forms.
Gemma is basically immortal because of his strange ability... and that is why he is the leader of the Devils of Kimon. With their help he hopes to become the "Shogun of the Dark", the ruthless new leader of the Japanese government who will rule the country with terror from the shadows. It's ironic that he's working for the Shogun of the dark, while he intended to betray him all along. A Devil in every sense of the word.
There is also a strange feud going on between Benisato, Yurimaru, and Zakuro because of Gemma. He is Benisato's lover, as well as Yurimaru's, which leads to Yurimaru's jealousy of Benisato. Zakuro lusts after Yurimaru. This jealousy and rage proves to be both important and fatal throughout the anime.