Kirisame

Kirisame (キリサメ) is a curved blade that Hody Jones uses underwater. This weapon made its first appearance in Chapter 637, in the sheathe behind Hody's back, and is seen being used in Chapter 638. The blade was broken by Luffy during their clash in the ocean.

Abilities
Hody puts the blade on his back (over his dorsal fin) to cut his opponents while swimming, further enhancing his shark features.

The blade is extremely sharp as it was able to cut through a large oarfish that was near him. Hody was also able to swim while somersaulting rapidly, in a manner similar to a buzzsaw.

Translation and Dub Issues
The term "Kirisame" (霧雨) is usually translated as "drizzle" or "misty rain", with "Kiri" meaning "mist" or "fog", while "same" meaning "rain", thus creating a pun.