The Black Demon series

The Black Demons are the most powerful cursed weapons of Owari no Seraph. In the mod, they rest at the bottom of the sealed armory, each planted in its gold-trimmed wooden chest beneath red sacred cords. They surpass Netherite in both damage and durability.

The seven weapons

Weapon	Form	Damage	Speed	Wielder in the anime
Asuramaru	Katana	10	1.8	Yūichirō Hyakuya
Kiseki-ō	Blade	9	2.2	Shihō Kimizuki
Gekkōin	Bow	—	—	Yoichi Saotome
Byakkomaru	Bayonet	9	1.6	Shinya Hīragi
Mahiru-no-Yo	Katana	11	1.7	Guren Ichinose
Raimeiki	Katana	10	1.8	Kureto Hīragi
Shikama Dōji	Scythe	13	1.1	Shinoa Hīragi

All of them: 3,200 durability (Gekkōin, a bow: 2,400), enchantability 20 for the blades, fire resistance, epic rarity, no repair by material. For comparison, a Netherite sword deals 8 damage at 1.6 and lasts 2,031 uses.

Getting them

1. Find the armory and go down to the weapon hall (y = -38).
2. Tear off every ofuda from the sealed gate.
3. Take a mass-produced weapon and feed it to the Demon Lock.
4. Go down to the vault (y = -55) and take the weapons from their pedestals.

Each armory holds one of each. They are also in the creative tab.