Specialties of all other katanas are stated clearly in the show, but the specialty of Nokogiri (seen in the picture below) wasn't explained clearly and in detail. What is the unique specialty of the katana Nokogiri which was under the possession of Zanki Kiguchi?
According to the Katanagatari wiki, the Nokogiri doesn't have any poison but has the ability to cure the effects of the poison from the other swords:
A wooden sword that sharply contrasts its title as "King of Swords", it is in the possession of Zanki Kiguchi. Unlike the other Deviant Blades, it doesn't have any of the poison found in Kiki's blades. It is the purest blade with the ability to cure the effects of the poison the other swords have on their owners. A small floral mark and yellowish streak on the sword identifies it as Nokogiri.
