Banryu is the sword used by the Shichinintai leader Bankotsu. Banryu is a powerful sword and Bankotsu adores the sword more than anything ( calling it his 'baby', 'companion' etc.).
As soon as Bankotsu was revived he went in search of Banryu and took it back from a castle where it had been stored. It is later cracked by one of Inuyasha's 'Kaze No Kizu' attacks but is then repaired and strengthened thanks to a handful of shikon shards.
During his last fight against InuYasha, he explains that he made a wish upon Banryu that it will get demonic power when he'll kill 1000 daimyos and 1000 youkais.
Bankotsu can use 'banryusen' and 'ryuuraisen' using Banryu.