In the 1600s, the battle of Seikigahara is fought between the Western Army and the Ieyasu Tokugawa's Eastern Army. During the battle, two samurai face off, one known as Kyoshiro, the other known as Demon Eyes Kyo (killer of a thousand men). As the battle rages on, an unexpected falling star crashes into the ground overwhelming both samurai. Years later, Kyoshiro, performs as a medicine man, roams the land with a past he can not recall. Soon, he realizes that he is not alone for his enemy's soul, Demon Eyes Kyo, is now within him. When Kyoshiro encounters the bounty hunter Yuya Shiina, an unexpected turn of events occur causing the sweet Kyoshiro to retreat having the soul of Demon Eyes Kyo take over the body of Kyoshiro. The world will soon discover why Kyo is called a demon!
The final battle between Oda Nobunaga and Demon Eyes Kyo.
Yukimura betrays his friends and joins the Mibu clan, and awakens the final Murimasa. Kyo finds him and starts a fight but can he kill a friend?
The warlike Kyo has now completely taken over Kyoshiro's body.He meets the charismatic samurai Yukimura Sanada at an in,and they are later attacked by a mysterious ninja girl, Mahiro.
Jimon, the Kenyou recalls his past encounter with Demon Eyes Kyo at the Battle of Sekigahara. He was defeated easily, and terrified by Kyo's red eyes. Left for dead, Jimon was later obliterated by the falling star. Now as a Kenyou, he wants to crush Kyo and exact his revenge. Kyo uses his sword, the Muramasa and his special technique, Mizuchi to destroy him easily though. Afterwards, Kyo chases Yuya and eventually changes back into Kyoshiro. Kyoshiro explains that Kyo is not who he really is and decides to head out on his own. Yuya however will not let him, saying that she wants to help someone in need (although she is in reality, after the bounty for Demon Eyes Kyo). On their way to a nearby village, Kyoshiro and Yuya run into Okuni, a former acquaintance of Kyoshiro's whom he does not remember. Okuni explains her past with Kyoshiro and Demon Eyes Kyo and how she longs to see Kyo. They arrive at the village the next day but Okuni has apparently disappeared. Kyoshiro and Yuya appear to have a warm welcome, but there are shady characters lurking about.
It turns out that the samurai village is being terrorized by a gang of hired assassins. One of them challenges Kyoshiro, thinking he is Demon Eyes Kyo. Benitora, another one of the gang changes sides to save him. Shirogarasu, the last remaining assassin, comes to challenge both Kyoshiro and Benitora. This new opponent is too strong, and Kyoshiro is forced to call upon the Demon Eyes Kyo's power.
The first episode shows Kyo and Kyoshiro battling each other while Yukimura Sanada, Sasuke Sarutobi, and Saizo Kirigakure arrive at the battle ground where Kyo and Kyoshiro continuing fighting. Meanwhile, Kyo destroys Kyoshire's sword and tells him that he lost and should give up. Then, Yukimura comes and tells them to stop because Sakuya creates a meteor raining down on the battle field. Then four years later, Kyoshiro meets Yuki and then a demon attacks them. The demon was actually a guy who fought in the war four years ago. The demon beats up Kyoshiro, but Kyo takes over his body. Kyo beats the crap out of the demon and then Kyoshiro takes back his body and continues to travel with Yuki by his side.
Lord Yukimora asks Sasuke to help demon eyes Kyo and the gang get to the opening of the forest of trees, but on the way Sasuke meets up with an old friend.
Yukimura convinces Kyo to enroll in the Shogun's tournament, where all the greatest fighters in japan are gathering. Kyo meets Migeira, a strange man from Europe who explains that Kyo's sword, a Muramasa blade, has special powers.
It all changes during the shogun's tournament when Lord Tokugawa attacks Kyo. We find out that the lord is a being controlled by one of Nobunaga's henchmen.
The gang follows Lord Tokugawa under the castle and Benitora discovers a Murimasa, but can he lean to wield it in time to save his friends?
Mahiro accuses Kyo for killing her sister, and attempts to take her revenge. During the battle, the truth of what happened is revealed and Kyo saves Mahiro from their common enemy.