InuYasha the Movie 3: Swords of an Honorable Ruler

is the third InuYasha movie. It was released on December 20, 2003 in Japan (between episodes 136 and 137) and in the United States on September 6, 2005.

Plot
On a snowy night near the ocean, blood drips from the left hand of the Inu no Taishō. His son and heir, Sesshōmaru, asks his father if he insists on going and asks for his two swords, Tessaiga and Sō'unga. But his father asks if he desires power so much, he must have someone to protect; Sesshōmaru says no, as he has no need for such. His father then transforms into his true dog form, running off. Myōga, clinging near his right eye, pleads his master to reconsider, for his wounds from his battle with Ryūkotsusei have not yet healed but the Inu no Taishō refuses, as he must reach his human wife, Izayoi, who is just giving birth to his second son, and that he doesn't believe he is long for this world.

At a mansion, guarded by many samurai, their leader, Takemaru of Setsuna, ignores the midwife's warnings and takes his spear, killing the midwife. Then he enters the birthing chamber as a lunar eclipse begins. He tells Izayoi, that he had always loved her but loathes the fact that her heart has been stolen by a demon and stabs her with a spear. As he leaves, he hears the cries of a newborn half demon.

At that moment, the Inu no Taishō arrives at the door, using his Kaze no Kizu to cut through the lines, despite being hit by a few arrows. After hearing that Takemaru slew Izayoi, he slices off the samurai's left arm and enters the mansion, just as Takemaru summons his men to set it aflame. Inside, the Inu no Taishō finds Izayoi and uses Tenseiga to revive her, and covers her with the Robe of the Fire Rat to protect her from the fire. Takemaru then approaches, determined to fight to the death. The Inu no Taishō draws his third sword, Sō’unga and tells Izayoi that their son shall be named Inuyasha and battles Takemaru as the mansion collapses on them. Izayoi, holding her infant son, escapes

In the present, Sō’unga is found to be a secret treasure of Kagome's family. Suddenly, the sword flies off to find the nearest demon, finding Inuyasha, who had followed Kagome to the present to make sure that no harm comes to her but she assures him in the future there are no demons. Sō’unga's sheath, Saya, says that Inuyasha must master the sword before it destroys the modern world. But instead, it takes possession of his arm and Inuyasha manages to convince it to return to the past.

Emerging from The Bone-Eater's Well, Sō’unga causes Inuyasha to revert to his demonic nature and attack a nearby village. Miroku and Sango stop him from hurting anyone as the villagers evacuate themselves. Inuyasha unleashes the sword's Dragon Twister, which is more deadly than the Backlash Wave, wreaking a huge amount of destruction, though Miroku and Sango avoid this on Kirara. Inuyasha then wanders off to rest whilst the sword is out of energy. In the meantime, Kagome returns to the past with Saya, who apparently knows Myōga.

Sō’unga brings Inuyasha to the territory of ogre demons, and slays three. Kagome and company later come upon them but the corpses awaken as the walking dead. Slashed, some parts still move and they are filled with miasma, which Miroku finds out when he sucks one in with his Wind Tunnel. Saya advises they use fire but Shippō's is too weak so Kagome purifies them. Only one orge leaves the skirmish.

Inuyasha soon meets up with Sesshōmaru, who is disgusted that the Sō’unga came into his possession. As the brothers do battle, whenever their blades clash, Sō’unga knows Sesshōmaru's every thoughts, especially that Inuyasha cut off his left arm. It evens taunts him, saying that if his father had listened to him, he wouldn't have met a miserable fate. Sesshōmaru grabs Tessaiga and uses the Kaze no Kizu in an attempt to silence the sword, severely burning his hand, but Inuyasha and Sō’unga survive. The sword, now angry, wishes for more blood and prompt Inuyasha to attack Rin and Jaken. but, before he was able to hurt them, Kagome told him to sit.

Kagome meets up with Tōtōsai, who also knows Saya. He explains that Sō’unga is a sword possessed by the spirit of an ancient evil demon. She uses her "sit" command to hold Inuyasha and grabs him, just as Sesshōmaru tries using his poison claw. Sō’unga flies away and the enchanted beads scatter. Leaving an unconscious Kagome behind, a guilty Inuyasha then goes off on his own to destroy the sword.

The undead ogre demon finds Sō’unga and attempts to pick it up but instead becomes its host. It goes into the netherworld and retrieves Sesshōmaru's left arm before coming to the gravesite of Takemaru. Calling out to Takemaru's forgotten soul, it promises revenge against the Inu no Taishō by killing his sons. Takemaru is resurrected and given the left arm to use the Dragon Twister. As he grasps the sword, he is given a demonic appearance, with Sō’unga's spirit represented as a purple smoke.

Elsewhere, Kagome awakens and finds that Rin and Jaken are with them, having been abandoned by Sesshōmaru. The old demons decide to tell the whole story concerning Sō’unga. After Inuyasha's father died, they were to undertake instructions according to his will; Myōga placed the Tessaiga in the master's remains and hid it in the black pearl; Tōtōsai made sure that Tenseiga was passed to Sesshōmaru; however, Saya said there were no instructions for Sō’unga. They couldn't give it to Sesshōmaru for he would kill them for giving him the previous sword, and Inuyasha was only an infant. Saya then proposed to hold the sword quietly for at least seven hundred years and have it thrown into the Bone Eater's Well. Now the only way to defeat Sō’unga is for both Inuyasha and Sesshōmaru to join forces but many seriously doubt that that will ever happen.

Both the brothers arrive at Takemaru's gravesite and Sesshōmaru decides since Inuyasha is unaware of the human's connection to Izayoi, he will die ignorant causing the two to draw swords against each other. Inuyasha tells his brother that since Tessaiga's barrier rejects him, he can't even pick it up, whilst Sesshōmaru would prefer the pleasure in killing the half-breed whose father's blood flows in his veins. Inuyasha then protested that he would destroy Sō’unga, however Sesshōmaru retorted that he doesn't even know what their father looked like. Inuyasha attempted to use the Backlash Wave against Sesshōmaru but he repelled it with his Dragon Strike. However, Inuyasha was protected by Tessaiga's sheath, prompting Sesshōmaru to leave.

Takemaru slays entire armies and an entire castle and using Sō’unga, he resurrects at least two thousand soldiers, making them his army of the undead. Kagome's group faces them in a titanic battle, with Inuyasha and Sesshōmaru also joining in on their own. Takemaru has one of the undead grab the Tenseiga, attempting to destroy it with gunpowder but it fails and the sword flies off. Rin finds it, but the undead ogre demon grabs her and Kagome and takes them to Takemaru, prompting Sesshōmaru and Inuyasha to follow. Sō’unga tells Takemaru that the girls are no different than Izayoi and the samurai proceeds to try and kill them, for those who consort with demons are all Izayoi in his eyes. Kagome is partially protected by Sō’unga's sheath and Rin is confident that Sesshōmaru will save them, which he does. The girls try to run, but their path is cut off by the ogre. It grabs Kagome, causing the enchanted beads to fall from her pockets. Rin throws one of them at it, disintegrating its head.

Outside, the others tells Inuyasha to rescue Kagome while they hold off the soldiers. But there are so many that many of their fire users got exhausted. Miroku uses his last resort: his Wind Tunnel, despite the danger to his body, sucking in all of the dead and becoming severely weakened.

Kagome tries throwing one of the beads at the headless ogre body but misses, however Inuyasha arrives and slices it in half. Kagome and Saya tell Inuyasha to join forces with Sesshōmaru to overcome Sō’unga's Dragon Twister but he refuses and runs off. Sesshōmaru fails in using Tenseiga to slay Takemaru, who is just resurrected by Sō’unga. Inuyasha then attempts to hit both of them but misses. Takemaru remarks that the half-demon looks like Izayoi and informs him of his part in her death. As they clash blades, Inuyasha is able to push Takemaru back. The latter and Sō’unga are bewildered at what they are seeing, for such power is impossible for a demon; Inuyasha retorts that he's half a demon and his human desire to protect someone is increasing his power and pushes Takemaru through a wall. Takemaru then has an epiphany that when Izayoi wanted him to leave, then he realizes that she was trying to protect him. He murmurs that he'd always loved her as his horn falls off and his flesh erodes, leaving only his skeleton. Sesshōmaru then slashes at the imps trying to resurrect him.

However, Sō’unga isn't finished. It causes the castle to collapse, crushing Takemaru's remains and creates its own body with the arm attached, opening a portal to the netherworld. Once the boundary between both worlds vanish, every living thing will wind up dead. Saya puts up a barrier to protect the nearby humans from being overcome by the dead souls from the netherworld, calling out to the living.

Inuyasha and Sesshōmaru battle with Sō’unga, each wanting to defeat the evil sword themselves. Kagome tells them to work together but they don't listen so she tries to purify Sō’unga but nearly gets killed. Inuyasha gives her his sheath to protect her as he tries to use the Backlash Wave to stop the Dragon Twister but it barely works. Sō’unga believes that he finished off the half-demon and turns to Sesshōmaru but Inuyasha gets up and uses the Backlash Wave again. Sesshōmaru remembers when his father asked if he had someone to protect and has short flashbacks of Rin and Jaken. Despite this, he stoutly claims he has no one to protect and combines his Dragon Strike with the Backlash Wave, overcoming the Dragon Twister and destroying Sō’unga's body, casting the sword into the netherworld.

The Inu no Taishō then appears, saying he's proud of them for sealing Sō’unga forever as the portal closes. Saya says that the master wanted his sons to work together, but they find that ridiculous. The other old demons ask Saya why he didn't speak up sooner; he claims he was just thinking of what's best for the brothers; but the truth is he really forgot.

In the post-credits, Kagome tricks Inuyasha into putting back on the enchanted beads, which she had managed to put back together thanks to Rin who collected all of its scattered beads, and in a soft tone of voice tells him to sit, ending the film.

Goofs

 * During a total lunar eclipse, when the moon is inside of the umbra, it should've been red due to the refraction of the sunlight by the Earth’s atmosphere into the shadow cone, but instead it was pitch black.
 * When Inuyasha was walking through the hole to finish Takemaru of Setsuna, the strap of his kimono was gone.
 * When Rin threw the Beads of Subjugation at the Zombified Oni, the spiritual power they possessed was strong enough to melt its head. However, when the rosary exploded earlier in the film, one of the beads was embedded in Jaken's forehead with no negative effects. Apart from losing consciousness, of course--but that was caused more by blunt impact than anything else (it knocked him right off his feet).
 * When sensing Sō'unga's arrival through the Bone Eater's Well, the Tōkijin was shaking instead of the Tenseiga.
 * In a scene during his ascent of the mansion to save Kagome after she was kidnapped by Takemaru, Inuyasha appears to have two Tessaigas: one drawn out in his hand, and the other inside its sheath. This scene is located right before Inuyasha runs into Sesshōmaru, after having just used the Wind Scar.
 * When Kagome yelled the "Sit" command to break Inuyasha out of Sō'unga's spell, Inuyasha should've been face first to the ground. Instead  he was on his back when the smoke cleared.

犬夜叉電影：天下霸道之劍