A sick looking karambit Nidhoeggr won on a random game of virtual slot machine one day. He likes to rub it in baki's face because it did not cost him any cash; he would also sell this sick karambit to buy more meaningful items.
The weapon itself does not give the user any benefits. It's just a sick looking karambit that costs a boatload of cash. Preferrably your mortgage. For the next 9 months.