Banryū

was Bankotsu's weapon.

History
Bankotsu wielded Banryū since before the Shichinintai was formed. After becoming the leader of the infamous mercenary group, Bankotsu continued to wield Banryū until he and the rest of the Shichinintai were executed. Banryū was kept by the feudal lord responsible for killing Bankotsu and his comrades as a testament to his achievement.

During the story
After the Shichinintai were revived by Naraku fifteen years later, Bankotsu and the others attacked the castle where Banryū was being kept. Bankotsu reclaimed Banryū and got his revenge by using it to kill the feudal lord and the Samurai general that were responsible for his execution.

Kōga and Inuyasha's group arrived at the castle after all of its habitants were killed. Bankotsu battled Inuyasha and his Tessaiga with Banryū. He managed to fight on equal terms with his weapon, but was overpowered when Inuyasha unleashed the Kaze no Kizu. Bankotsu survived thanks to the timely intervention by Ginkotsu, but his Banryū received a large scar from the attack. The Shichinintai were forced to retreat soon after and arrived near Mount Hakurei. They were greeted by Kohaku and Kanna, with the latter telling Bankotsu that he could make his weapon much stronger than it currently was. Bankotsu forced Renkotsu to forfeit the four Shikon Jewel shards that were stolen from Kagome, and embedded them into Banryū through its scar, reparing it and increasing its power.

Bankotsu confronted Inuyasha once again at Hijiri island. He had the upper hand due to Inuyasha's demonic powers being suppressed by the purifying barrier around the island. After the barrier was destroyed, Inuyasha regained his powers and unleashed the Kaze no Kizu, but Bankotsu was able to counter it with Banryū's new powers from the Shikon Jewel shards. Bankotsu continued to display Banryū's new abilities by using Ryūraisen to strike Inuyasha and the others with lighting. Despite Banryū's newfound powers, Bankotsu was forced to retreat with the aid of Saint Hakushin.

Inuyasha confronted Bankotsu one last time inside Mount Hakurei. Both of them were able to fight at full power due to the disappearance of the mountain's purifying barrier. Bankotsu managed to counter Inuyasha's Kaze no Kizu with Banryū's powers. After killing ten of Naraku's yōkai that were watching the fight, Banryū transformed and possessed a demonic aura. Bankotsu explained that it was due to a wish he made on Banryū that involved killing 1,000 humans and 1,000 yōkai, as well as the Shikon Jewel shards that were embedded in it. Ultimately, this would prove to be Bankotsu's undoing when Inuyasha was able to strike at him at full-force with the Bakuryūha. The attack destroyed Banryū and killed Bankotsu.

Physical description
Banryū is an incredibly large halberd rivaling the strength and size of Inuyasha's Tessaiga. Its blade resembles that of a large double-edged sword, and wide enough to act as an emergency shield. Its pommel has a large, crescent moon like design. Due to its large size, Bankotsu is the only known human to wield it effortlessly, as it takes at least three men to haul it around. Even so, it has its limits as it is damaged by Inuyasha's Kaze no Kizu.

Attacks

 * Bankotsu can summon a thunderstorm and manipulate the lightning, creating many lethal electric bolts that almost kills everyone on Hijiri island. The attack cannot be adequately controlled and hits randomly.
 * Kenatsu (剣圧, "Sword Pressure"): After embedding the four Shikon Jewel shards he took from Renkotsu, Banryū became empowered by their energy, allowing Bankotsu to project the energy from Banryū with simple slashes. He goes on to use this after gaining all seven Shikon Jewel shards from his deceased Shichinintai, and after Banryū gains demonic power.
 * By channeling the energy of the Shikon Jewel shards embedded in Banryū, Bankotsu can use an attack that is almost identical to Inuyasha's Kaze no Kizu, except it's pink in color, but matches its strength.
 * After embedding the Shikon Jewel shards of his deceased Shichinintai comrades into his body, Bankotsu is able to unleash a blast of heat similar in appearance to Inuyasha's Kaze no Kizu, except that it is red and can match it.
 * Bankotsu uses this attack during his final confrontation with Inuyasha in the caves of Mount Hakurei. He swings his Banryū and unleashes a wave of red energy that is strong enough to cancel Inuyasha's Kaze no Kizu.
 * Bankotsu's most powerful attack. The hatred of 1,000 humans and 1,000 yōkai built inside Banryū, combined with the power of the four Shikon Jewel shards embedded in the halberd, creates a huge and powerful ball of swirling, fiery yōki. However, this all-powerful attack is ultimately his downfall: because it is flowing with demonic energy, Inuyasha is able to use the Bakuryūha to reflect the attack back at Bankotsu, shattering the Banryū and defeating him soundly.

Manga vs. Anime

 * Most of Banryū's attacks that Bankotsu uses against Inuyasha in Episode 113 do not exist in the manga.
 * In the anime, it is revealed that Bankotsu made a wish on the halberd; should he slay a 1,000 yōkai and 1,000 humans and bask Banryū's blade in their blood, it would gain terrible demonic powers. In the manga, Banryū never obtains its demonic powers during Bankotsu's last fight with Inuyasha.
 * In the manga, Banryū stays intact despite Bankotsu's death. After having it's Shikon Jewel shards taken by Naraku, it is seemingly destroyed in the destruction of Mount Hakurei.

Trivia

 * Despite the fact that the English version anime and the manga refer to Banryū as a halberd, which is a European styled pole-axe, it has no resemblance to it, and more resembles a  crossed with a Polearm. In the Japanese text for the series the weapon is referred to as a polearm, presumably due to its giant size and length.
 * Banryū's Theme-Music from the InuYasha Official Soundtrack, Vol. 3 is entitled.
 * In the anime, It is suggested by Inuyasha that Banryū, after its transformation into a demonic blade, would have eventually destroyed Bankotsu due to being exposed to its intense demonic aura. This is possibly a reference to what happened to Kaijinbō when he was possessed by Tōkijin, which Banryū was also subsequently compared to.
 * At the end of Episode 111, it shows Bankotsu inserting the 4 shards that Renkotsu stole from Kagome into Banryū (one of which was the large shard Kagome and Kikyō fused from Kagome's 3 shards in Episode 98), making a total of 6 sacred jewel shards in Banryū. In Episode 113 however, Kagome states that there are only 2 shards in the halberd. (however, Episode 98, being an anime-only episode, would explain this discrepancy.)
 * It took three strong men to carry Banryū around, while Bankotsu is able to lift it with one hand without fail.