Inuyasha's party hides in a cave with a barrier, but the mirror demon finds them and breaks through it. As Inuyasha fights it, his body goes into demon form but Inuyasha somehow maintains control of his senses. As he wounds the demon, they are transferred to Kanna, who is controlling it. Watching from a safe place, Naraku orders her to keep the demon going until it kills them, or until their party kills her by killing the mirror demon. Inuyasha switches his target to the replica Tetsusaiga and successfully breaks it, which restores the power to his own sword and his body to his normal half-demon state. Kanna gets closer to the group, but Inuyasha refuses to kill her. Naraku makes Kanna and the mirror explode in a shower of glass shards in an attempt to wound the party. One shard of glass enters Kagome's eye. Through it, the dead Kanna gives her a clue as to how they can kill Naraku.

During a new moon, Sango and Miroku face off against a "Bone-collecting" demon. During the battle, Miroku is forced to use his wind tunnel twice, resulting in his being poisoned. To protect him, Sango coats her hiraikotsu in poison and uses it to destroy the demon, destroying her weapon in the process. Myouga suggests they visit the Demon Master of Potions to have it repaired. The drunken man agrees to repair it and dumps it in a jug of alcohol, dissolving it. He sends Sango into another jug to pacify the demons inside. The demon's are the hiraikotsu which want Sango to promise not to "betray" them again, but she refuses, saying that as she loves Miroku, she would sacrifice her life for him. Outside the jar, the Master of Potions offers Miroku a poisonous drink that will prevent him from feeling the pain of any other poison or demon miasma, though it will not prevent it from actually reaching his heart. The hiraikotsu initially intend to kill Sango, but Miroku drinks the poison so he can continue to protect Sango. The hiraikotsu demons agree to fight with her again, and Sango's weapon is restored, more powerful than before.

The demon Shishinki approaches Sesshomaru for a fight, having been defeated by Sesshomaru's father long ago. To Sesshomaru's surprise, Shishinki attacks him using a complete Meido Zangetsuha and claims Sesshomaru's father stole the technique from him. Sesshomaru attacks with his Meido, but Shishinki's absorbs it. Inuyasha and his group arrive and after Shishinki attacks him, Inuyasha joins the argument. Shishinki taunts Sesshomaru, telling him that he must have been shunned by his father if his half-human brother has Tetsuiga as Tensaiga is just a cast off from it to contain the unneeded Meido. As Sesshomaru furiously wonders why his father did this, Shishinki attacks again. Inuyasha protects him with the Wind Scar, but Sesshomaru punches him and tells him not to interfere. Sesshomaru blindly charges Shishinki. Miroku uses a paper charm to fire Myoga at Inuyasha so he can explain to Sesshomaru that his father entrusted him with the Meido because he felt Sesshomaru could master it, however Shishinki points out that he could have just given him Tetsuiga instead of casting off Tenseiga. Sesshomaru resumes his attack. When Inuyasha again comes to his aid, their swords begin pulsating. When Sesshomaru draws Tenseiga, he is able to launch a massive complete Meido that swallows Shishinki. Inuyasha tries to tell Sesshomaru that Shishinki was lying, and that Tenseiga is a proper keepsake, but Sesshomaru states that they are destined to fight one another the rest of their lives. Myoga states Sesshomaru must have realized his father's true intentions.

Sesshomaru visits Totosai, who confirms that his father gave him Tenseiga so Sesshomaru could perfect the Meido Zangetsuha before he planned Inu Yasha to reabsorb Tenseiga back into the Tetsusaiga. Meanwhile, Naraku begins pursuing Kohaku to retrieve his jewel shards, however Kohaku's shards are still being protected by Kikyo's powers and remain too pure for Naraku to easily get. Inuyasha's group arrives, and Naraku taunts Sango by saying Kohaku runs from her to forget his past. She states that she already knew that, but will still fight for him when he needs her. She attacks with Hiraikotsu and to her surprise, it now has its own demonic energy and it is able to injure Naraku. Inuyasha follows up with an Adamant Barrage attack, Kagome fires one of her arrows, and Miroku attempts to use his wind tunnel, but the injured Naraku manages to flee. Afterwards, Kohaku tells them that because his shards are still pure, they may be useable in the battle with Naraku. The injured Naraku orders Byakuya to give Sesshomaru a fragment of Kanna's mirror. In the end, Miroku examines that his miasma wound had spread due to using his wind tunnel while fighting.

Seshomaru challanges Inuyasha in order to see if Inuyasha is worth having Tetsusaiga. He uses a fragment of Kanna's mirror to create a replica of the sword from Tenseiga. The fight between the two takes place in an uncertain place where Naraku sends them for the first part.The second part of the battle is taken inside a Meidou Sangetsuha created by Seshomaru and is rather between Inuyasha+Seshomaru against the sword that is now manipulated by Naraku. Inside the meidou Inuyasha mannages to defeat the meidou by using the dragon scaled Tetsuaiga to cut his own yuketsu. That convinces Seshomaru that he is the true heir of the sword and when Naraku attacks Inuyasha he decides to help him, but not directly. In the end Tetsuaiga gets the Meidou ability from Tenseiga and that is how Inuyasha and Seshomaru manage to exit the meidou. The episode ends with Seshomaru's group and Inuyasha's parting.

Inuyasha's group returns to Kaede's village to tell her of Kikyo's death. As they talk, she states that Kagome's power was probably sealed by Magatsuhi, the evil will of the Shikon Jewel that did it out of fear of Kagome's powers. Meanwhile, Naraku enables Magatsuhi to manifest as a demon. With his new body, Magatsuhi attacks Sesshomaru's group to try to take Kohaku's shard. Sesshomaru struggles to defend the boy without a weapon and having only one arm. Inuyasha's group arrives to find Sesshomaru's right arm badly wounded and Kohaku's shard being defiled. As Inuyasha confronts Magatsuhi, he renders Kagome unconscious. Sesshomaru uses his will to heal his wounds, annoyed at Inuyasha's telling him to backdown, and assumes his true form to attack Magatsuhi. The brothers struggle to battle Magatsuhi, while protecting their respective groups. Eventually Magatsuhi spears Sesshomaru and traps him, saying he will be come part of Naraku's body. The others fear he is dead, and when Inuyasha rushes to free him he is captured as well. Sesshomaru bursts through the ball of appendages, and as Totosai arrives, Sesshomaru's left arm is restored and he is wielding a new sword. Totosai calls it Bakusaiga and says it was always inside Sesshomaru, but could not be wielded until he surpassed his father and learned let go of his obsession with Tetsusaiga. Kagome finally awakens.

Kohaku remains unconscious after being stared down by Magatsuhi, the evil will. Kagome is worried, but she has to buckle down and study for her entrance exams, so she decides to return home.

Sesshomaru chases after the evil will, Magatsuhi. But it’s only part of a trap set up by Byakuya of the Dreams. Magatsuhi finds Kohaku lying unconscious, and he tries to deliver his Shikon shard to Naraku.

Kohaku successfully drives Magatsuhi out of his body just as Sesshomaru arrives, who manages to cut Magatsuhi in half, destroying part of him. Naraku then tries to take Kohaku's shard himself, but Sesshomaru attacks with his Bakusaiga, which causes Naraku's body to explode. Meanwhile, a red aura passes from Miroku's body into Rin's. Now possessed by Magatsuhi, Rin flies off with a demon. Later, Naraku manages to capture Kagome and demands Inuyasha's group give him Kohaku's shard in exchange for her. Kohaku spots a sacred arrow on the ground and hides it, before offering himself to Naraku. When Naraku grabs him, Kohaku stabs the arrow into the spot where Moryomaru's diamond armor is, shattering it. Naraku escapes in a miasma cloud. Sango and Kohaku hug one another in celebration, but then a piece of Naraku's flesh stabs Kohaku in the neck and takes the shard, leaving Kohaku's empty body behind. Naraku completes the Shikon Jewel, but Kohaku is brought back to life by Kikyo's light after he hears Sango crying for him.

Inuyasha's group leave to defeat Naraku, leaving Shippo behind. As they find Naraku and Byakuya in a cloud of miasma, they see Sesshomaru enter Naraku's body in search of Rin. As Inuyasha's group enters, Miroku pauses to propose to Sango. They soon realize that though they are breathing in the miasma, it is not harming them because the Shikon Jewel wants to capture their souls first. Kagome and Inuyasha search for the defiled jewel, after Miroku and Sango are captured. As Inuyasha gets closer to the jewel, he turns into a full-blooded demon and attacks Kagaome. Naraku offers Kagome a miasma-coated arrow to save herself with, but she refuses. Inuyasha attacks again, throwing her off a cliff. Naraku says Inuyasha will kill her, just as he killed Kikyo.

Inuyasha’s heart is devoured by the Shikon Jewel’s poison, and he turns into his demon form helpless as the darkness in his heart takes control of him.

Kagome’s spiritual powers are restored, and divine light is revived in Naraku’s Shikon Jewel. However, Naraku uses this as a decoy to lure Sango into his trap.

Naraku has been living as a demon despite having a human heart. While fighting him, Kagome asks about his true wish.

Naraku heads for the Bone Eater’s Well and vanishes! Before disappearing, Naraku makes his last wish for Kagome, injured at the hands of Byakuya, to be swallowed into Meido, the Path to the Underworld.