They collect souls of people that etheir have eaten other people's souls or have done a deed so bad that the the shinigami demand their soul. Most are a two people team. One a weapon miester, in charge of making the weapon the shingamis' ultimate weapon, and the other is the weapon. The weapon can turn into a human and into a weapon. Their are different forms of weapons. Example, swords, scythes, guns, and any weapon.