Bakusaiga

is a sword that was created from Sesshomaru's own body. The Bakusaiga came from Sesshomaru's body attached to his finally regenerated arm. It is nearly unique in that it is one of two yokai swords in the InuYasha universe not forged from a yokai's fang. It is Sesshomaru's final signature sword.

History
After shattering the Tokijin in combat with Mouryoumaru (Manga Chapter 407) and passing Tenseiga's only offensive technique Meidou Zangetsuha to Inuyasha's Tetsusaiga (Manga Chapter 503) Sesshomaru is left without a fighting weapon beyond his own native abilities. While very few demons stand a realistic chance against an unarmed Sesshomaru, the growing darkness in the Shikon no Tama allows a demon called Magatsuhi to escape from the jewel itself. Freed, Magatsuhi assembles a body from parts of Naraku and seeks out Sesshomaru in order to steal the last shard of the jewel from Kohaku, who is traveling with Sesshomaru. Sesshomaru accepts the challenge of battle and discovers that Magatsuhi has a poison that can physically damage him. The fight is interrupted by the arrival of Inuyasha, who comes to his aid. Sesshomaru, angered by the implication of weakness inherent in the help and pity he receives from both his own followers and Inuyasha's group, manifests a powerful regenerative ability composed of demonic power, caused by his pure fighting spirit, to force his wounds closed. The battle is again joined, and the use of Tenseiga against the otherworldly spirit of Magatsuhi offers hope of victory, but Sesshomaru is stabbed straight through his armor and chest by Magatsuhi. While he is engulfed by a mass of demonic flesh controlled by Magatsuhi, Inuyasha makes a desperate attempt to free him but only gets caught in the engulfing mass himself.

At this point, all parties are shocked to see the demonic mass blown apart by a massive burst of demonic power. The light is so blinding it takes several seconds for the group to see that the light, is in fact, coming from Sesshomaru severed arm. Sesshomaru, angry, drives back Magatsuhi's probes. At this moment the sword smith Totosai appears. Sesshomaru, seeing him and realizing in that instant what is happening, meets a massive thrust by Magatsuhi with an even more powerful wave of light - in that instant, within the light his arm regenerates and along with it a sword appears in the new hand. Bakusaiga was formed from Sesshomaru's previous left arm that Inuyasha cut off with his sword in Episode 8.

Magatsuhi attempts to reassemble his body. However, he discovers that pieces of his body attacked by the new sword not only get destroyed, but also transmit the blow they have received to undamaged parts - his body is destroyed attempting to reform.

In the course of the final stages of the battle Totosai reveals that the new sword is called Bakusaiga. It is not an heirloom or crafted sword but is created from Sesshomaru's own body as a manifestation of his own demonic power, and thus truly his own. His success in abandoning his interest in stealing Tetsusaiga as a quick path to power resulted in the development of his own inner strength, in the end surpassing even that of his father and the two swords derived from him.

Sesshomaru uses Bakusaiga for the rest of the series to battle both Naraku and Magatsuhi. During the Final Battle against Naraku, the Bakusaiga destroys most of Naraku's body. In the final chapter, set three years after Naraku's defeat, the Bakusaiga is still carried by Sesshomaru. It is arguably the strongest sword in the Inuyasha Anime. It is also noted that Sesshomaru could have obliterated both Inuyasha and Naraku at various times with the Bakusaiga, but chose not to do so. He began to understand that he could not use such power recklessly, and acted swiftly to save Kagome as well as Rin.

Appearance
Bakusaiga takes on the form of a katana with a unique design. The backside of its blade features various rune-like lines running along it with a beige hilt featuring the same design.

Powers & Abilities
It is because of this particular feature that Bakusaiga proved to be a bane to Naraku, as it prevented him from absorbing or reabsorbing demons or parts of himself that were cut by the sword without risking being destroyed himself. Only the Shikon Jewel itself withstood any Bakusaiga attack. Due to being created from Sesshomaru's body, the sword's ability seems to be an enhanced version of Sesshomaru's poison claws.
 * Explosive Corrosion Wave - Bakusaiga is able to fire off explosive green-colored waves of energy that capable of annihilating thousands of demons with a single cut. Not only does it disintegrate the main body, but the disintegration effects would also spread over to parts detached as well, as if it were Sesshomaru's acidic poison taking on the form of energy.

What Inu no Taisho believed....
Inu no Taisho, Sesshomaru and Inuyasha's father, believed that Sesshomaru would be able to surpass the powers of Tessaiga and himself if only Sesshomaru let go of the grudge against his will of giving Tessaiga to Inuyasha as well as giving Tensaiga, the sword that "will not cut", to Sesshomaru. Thus, Sesshomaru was only be able to let go once he was battling Maguhstuhi. From then on, Sesshomaru has inherited the Great Dog Demon's title. Bakusaiga as any sword would, matched the personality of its master, Sesshomaru; the cruel streak of killing thousands at once. (As mentioned by a monk in the episode of 'Forever with Lord Sesshomaru' who saved Rin from the kiddnapping youkai, Sesshomaru seems to have a very strong desire to kill, but it does not seem in the outside in his actions.... at times when many challenges him, but Sesshomaru at times ignores the challenge of people like his younger brother, Inuyasha.

Trivia

 * Having been able destroy most of Naraku's body, even when being held back, Bakusaiga may very well be the most powerful item/weapon in the series, only rivaled by the Shikon Jewel.