Just a thought.

Soul Eater Wiki wrote:All Demon Weapons have the ability to consume human souls, but should a Weapon consume a pure human soul (as opposed to a corrupted souls) their souls will become corrupted, and they become a Dark Weapon. Such Weapons are on their way to becoming a Kishin and are especially dangerous. Dark Weapons, due to consuming pure souls, are also in danger of falling into Madness.

Dark Weapons are born of the particular individual's fears and although these vary greatly dependent largely on the past events of the specific weapon, it is the succumbing to these vices which begins the descent towards becoming a Kishin. Eventually the weapon's desperation to be rid of these fears, develops into an insatiable craving for power that inevitably drives them to consuming the soul of a good human. The ingestion of such a pure soul corrupts the weapon in question, meaning that even with the substantial boost in power afforded by the act, they find that neither their fears or hunger are quenched in the slightest. This begins a vicious cycle in the consumption of a significant amount of human souls, until they either achieve the status of a Kishin or are hunted down and killed at the hands of Shibusen.

A dark weapon that consumes 99 human souls and 1 witch soul can transform into a Demon Sword, which is equivalent in power to a Death Scythe (Weapon). The only known surviving Demon Sword is Ragnarok.