The Eight Arms

The Eight Arms are a set of eight katana in total, wielded by the captain of the Ika Bounty Hunters, Ika himself. These are special swords due to the fact that all eight are forged from seastone, making them effective against Devil Fruit users; especially Logia types.

Trivia

 * A possible name I had for The Eight Arms was "The Eight Paths," a name inspired by the title "The Six Paths of Pain" from the Naruto series.
 * The Eight Arms are a reference to its wielder's Devil Fruit power and name. Ika means squid in Japanese. Squids have eight tentacles. Ika's Devil Fruit power allows him to become a Black Widow. Black Widows have eight legs.