Samehada ("Shark skin") is Kisame Hoshigaki's sword. It is covered in dark blue scales, but is usually hidden in a sheath of bandages, and worn on Kisame's back. As one of the former "Seven Swordsman of the Mist" (of the Village Hidden in the Mist), only Kisame is able to wield Samehada - It will hurt anyone else that tries to touch it, and return to Kisame. As well, it absorbs the opponent's chakra when it makes contact; it can presumably do so until they have none left. Because it is covered in rough fins, it shreads a target, rather than slicing it. It also seems to be able to attack while still fully-covered in bandages, though they will come off during the attack.
SameHada now is in possession of Killer Bee. It fell in love with Killer Bee's chakra after the battle between him and Kisame and decided to be Bee's sword instead.