Rasetsumaru is a character from Samurai Shodown V, made up to be an evil counterpart to Haohmaru, though the two aren't related.
Rasetsumaru is a bloodthirsty demon who escaped from Makai. He started a killing spree, his sword becoming red from the blood of his victims. He eventually heard about Haohmaru, a warrior who looked exactly like him, so Rasetsumaru went after him to kill him and eat his heart to become whole. He eventually found Haohmaru and attacked him, but it turned out to be a nun in disguise, who proceeded to decapitate him. Though he is implied to be dead, the last scene shows his disembodied head laughing.