Bakusaiga

is a sword that was created from Sesshōmaru's own body. The Bakusaiga came from Sesshomaru's body attached to his finally regenerated arm. It is Sesshōmaru's final signature sword.

History
After shattering the Tōkijin in combat with Mōryōmaru (Manga Chapter 407) and passing Tenseiga's only offensive technique Meidō Zangetsuha to Inuyasha's Tessaiga (Manga Chapter 503) Sesshōmaru is left without a fighting weapon beyond his own native abilities. While very few demons stand a realistic chance against an unarmed Sesshōmaru, 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 Sesshōmaru in order to steal the last shard of the jewel from Kohaku, who is traveling with Sesshōmaru. Sesshōmaru 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. Sesshōmaru, 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 Sesshōmaru 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 Sesshōmaru's severed arm. Sesshōmaru, angry, drives back Magatsuhi's probes. At this moment the sword smith Tōtōsai appears. Sesshōmaru, 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 Sesshōmaru's previous left arm that Inuyasha cut off with his sword in Episode 7.

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 Tōtōsai reveals that the new sword is called Bakusaiga. It is not an heirloom or crafted sword but is created from Sesshōmaru's own body as a manifestation of his own demonic power, and thus truly his own. His success in abandoning his interest in stealing Tessaiga 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.

Sesshōmaru 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 Sesshōmaru. It is arguably the strongest sword in the Inuyasha Anime. It is also noted that Sesshōmaru 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

 * Explosive Corrosion Wave - Bakusaiga is able to fire off explosive green-colored waves of energy that capable of annihilating a thousand weak yokai with a single swing (though this is likely hyperbole). Not only does it disintegrate the main body, but the disintegration effects would also spread over to parts detached as well, similar to energy transfer, though its effects are useless against opponents strong enough to resist the remaining energy output. It is because of this particular feature that Bakusaiga proved to be a bane to Naraku, as it prevented him from absorbing or reabsorbing yokai or parts of himself that were cut by the sword without risking being destroyed himself. Only the Shikon Jewel itself withstood any Bakusaiga attack.

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

Trivia

 * Having been able to 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.  On the other hand, Bakusaiga has only shown one powerful attack technique (though this attack is clearly more devastating in terms of scale than any in the series).  It's ability to affect barriers (whether demonic or holy) has not been tested and it is unknown if it would destroy Tessaiga on contact (or if Tessiaga would be able to break it and absorb its' attacks).  However, these may be unnecessary since Sesshōmaru has ceased his rivalry with Inuyasha and has shown considerable resistance to various barriers.

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