The godslayers, sometimes specifically called the godslaying weapons to differentiate between someone who kills gods and the weapons themselves, are nine legendary weapons crafted just prior to the Godbomb.
Little is known of the godslayers, though many of them have myths surrounding their creation. What is known of them is that they were somehow created from the body parts of gods (as evidenced by the godslayers themselves saying things such as, "I was forged from your ancestor's fang") and that each of the weapons has a different creator, but their creation overall seems to have been directed or at least spurred by Konec Aniklý (also the creator of Ganrikkat, the Timeripper).
Godslayers can only be used by those with godsblood -- that is, direct descendents of gods. Anyone without godsblood who touches a godslayer directly will be burned. Sabarus alphas, though, will not feel any pain by touching a godslayer, but a godslayer in their possession will immediately deactivate and cannot be used to their full potential.
The godslayers originally had their creators' spirits sealed inside of them; however, years of different wielders have caused all but Eiorozziore (and possibly Ganrikkat) to retain their original consciousnesses.
Godslayers have powers far beyond that of any normal weapon. They give off immense amounts of Chrono and each have a particular ability unique to that godslayer (such as Eiorozziore's ability to coat its wielder with an energy shield and Ganrikkat's ability to transport its wielder throughout time). However, their true power can only be awakened by speaking an incantation unique to that godslayer, which the weapon will tell its new wielder.
Godslayers possess the ability to talk and are fully sentient. Their personalities vary on account of the different people sealed inside of each weapon.
Being hit with a mortal, death-dealing strike while holding an active godslayer will cause its wielder to go into an "avatar" state. In an avatar state, the wielder is possessed by the spirit of the weapon and gains heightened, god-like powers. However, if they truly die while in the avatar state, they will become the new spirit that inhabits the weapon, ousting the previous one and being trapped in the weapon themselves.
According to a comment made by Eiorozziore during the second dream of Arplakoon, being forced into the avatar state while wielding two godslaying weapons will cause the weapon that is most compatible with one's lineage (i.e. most closely related to the god that the wielder is descended from) to take over the wielder. It is impossible to activate two avatar states at once.
List of Godslayers
Eiorozziore, the Godbreaker.
Feivelkt, the Blazing Phoenix.
Jadern Istrat Hnev, God's Final Breath.
Ganrikkat, the Timeripper.
Lagrímala, the Last Tear.
Zwehan Kut, the New King.
Ji Lhan, Reality's Edge.
Oladani, Destruction Lust.
Nascimedo, Fear's Birth.