Might want to add some other descriptions aside Friede's Scythe.
Attire of the three mentors of the Sable Church of Londor...
..this billed mask belongs to Yuria, the second eldest.
These maidens of a Primordial Serpent were renowned as founders of the Sable Church, which offered salvation for Hollows.
It is apparent that the women in black were highly skilled fencers, capable of founding the Sable Church between just the three of them
This Is Where It is stated the 3 sisters were fencers
Next We Have Yuria's Weapon
A cursed sword with an unseen blade, the choice weapon of Yuria of Londor.
Yuria, a mentor of the Sable Church and accomplished swordswoman, is said to have claimed a hundred lives with this weapon.
Seeing as Yuria Had a Specific Sword associated to her It could be safe to assume Friede had one as well.
Elfriede, the eldest amongst her sisters and leader of the Sable Church, bestowed this sword to her knight. Only, the sword was a farewell gift, and acceptance signified the knight's resignation from Elfriede's service.
My guess is that the Onyx Blade might have been Friede's Sword and she gifted it to Vilhem when She left the Sable Church.
After renouncing everything, Friede discovered a people that she wished to protect, and assumed the precise form that they yearned for
By Reading Friede's Garb we see she renounced everything, this i why I assume she gave her sword to Vilhelm. It could also explain why she abandoned swordsman ship. Seeing as she assumed the precise form the people she wished to protect yearned for. Knowing that the people she served were Corvians lead to the last item in this list.
The Great Corvian Scythe States,
Great scythe of the forlorn souls guided by heretical storytellers. The Mistress of the Painted World is said to wield a great scythe herself. Great scythes inflict profuse bleeding, such that the blood splatters on the wielder.
As shown in the Corvian Scythe Description The Mistress of the painted world wields a Great Scythe, showing that the Form she chose to adopt wielded a Scythe.
Hope this helps in your question