Izumo and Ashura kill each other in combat, but believe they will spend paradise together. Izumo's master and Ashura's assistant writes the story of the starcrossed lovers.
A group of highly-skilled demon wardens patrol ancient Japan, slaying demons who have possessed people. One night, the leader of the demon wardens encounters a demon priestess, Bizan, who foretells the coming of Ashura the demon queen. Some time later, the leader and his two trusted lieutenants, Izumo Wakaraba (Somegoro Ichikawa) and Jaku Abe arrive at a town utterly infested with demons. While the three begin slaughtering the demons, Izumo hears a ghostly voice calling out to him. He follows the voice and a trail of red flower petals to an abandoned building with a young ten-year old girl. The voice tells him the girl is a demon, so he slaughters her, but he spills only human blood.
Five years later, we discover that Izumo has retired from being a demon warden and works as the lead actor for a kabuki theater, with a master who is out of ideas for new plays. The town is assaulted by a group of ninjas. Izumo stumbles upon one of the ninjas, an attractive woman, and steals her hairpin. She later finds him and tries to steal her hairpin back, but he uses ancient magic to bind them together. The woman, named Tsubaki (Rie Miyazawa) has amnesia and remembers nothing of her past. She has a tattoo of a red flower on her back shoulder. Meanwhile, the demon wardens locate Bizan and prepares to slaughter her. Bizan, however, promises Ashura's power to the strongest warrior, so Jaku betrays his clan and kills the leader of the demon wardens, while Bizan's demons destroy the rest of them. Bizan and Jaku have sex, and prepare to locate Ashura's host body.
Izumo and Tsubaki grow closer, although her tattoo occassionally burns her and anyone who touches her. Jaku attempts to kidnap Tsubaki, and is repelled by Izumo who promises to be her bodyguard. Izumo's master, impressed that Izumo used to be a demon warden, begins following him covertly and writing down Izumo's adventures. Eventually, Tsubaki is captured by Jaku, but Bizan allows Izumo to rescue her. After her rescue, the two confess their love for each other and have sex (with Tsubaki licking Izumo's wounds). That night, a spectral voice calls to Tsubaki, and she goes towards it, followed by Izumo. They arrive in the house where Izumo slaughtered the young child.
Once there, Tsubaki's flower tattoo ignites her whole body, badly wounding Izumo and imprinting her flower tattoo onto his skin as well. Bizan appears and says that Tsubaki is the young girl that Izumo killed five years earlier. She says that for Ashura to be released from her human form, she needed to be killed by a demon warden as a child, and then have a human ignite her passion through the power of true love. Izumo has done both of these things, with Tsubaki having sprouted forth from the girl's dead body. Tsubaki continues to change into Ashura, and says she hates Izumo for awakening her demon spirit. Jaku tries to kill Izumo, but is defeated and mortally wounded. Ashura opens the portal to the demon world (a bridge composed of red flower petals) and she, Bizan and Jaku flee to the demon world as Izumo passes out from his wounds.
Once there, Ashura's flying castle descends over Edo and begins firebombing it, while Ashura revives Jaku with her demon powers. Izumo prepares for his final battle and his master is not allowed to follow. Izumo slaughters dozens of demons before confronting Jaku once again. Jaku grabs Izumo and reveals that his super-powerred grip prevents Izumo from breaking free. Bizan appears and attempts to stab Izumo, but at that moment Ashura recalls her powers, allowing Izumo to dodge the blow and causing Bizan to fatally stab Jaku. Izumo then slices Bizan with his sword, killing her.
Finally, Izumo confronts Ashura, who quickly gains the upper hand and wounds Izumo. She soon discovers, however, that they are still linked, both by the binding spell between Izumo and Tsubaki and by the tattoo they both share. Ashura is also touched that Izumo kept Tsubaki's hairpin this whole time. Ashura realizes that Izumo can only die if she does. The two combatants embrace, planning to finally be together forever in the afterlife. Ashura then bites through Izumo's neck while he fatally stabs her through the heart. Ashura's castle explodes, killing all inside.
At the end we see Izumo's master writing the tale of Ashura and Izumo beneath a flowered-tree. We find one of Ashura's demons working with him to fill in the details of the tragic story.
Thanks Evan B!