Augus' (Asura's Wrath) greatest weapon is Wailing Dark, a sword powerful enough to battle against Six-Armed Vajra Asura and Deus, unleash energy slashes powerful enough to raise a chunk of the Moon, and literally cut through the Earth itself.
By surrounding his hand in his Godly ki, Zamasu (Dragon Ball Super) can create God Split Cut, an energy powerful enough to kill large beings and gods.
The Dark Knight Sparda (Devil May Cry) is a legendary demon who once wielded the weapon named after him, an indestructible sword imbued with his own demonic power.
Kain (Legacy of Kain series) wielding the Soul Reaver, a blade that steals the souls of those it kills. Forged as the prophesized weapon of the Scion of Balance, it is the only weapon capable of harming the Elder God.
Ryu Hayabusa (Ninja Gaiden series) wields of the Dragon Sword, blade carved from the fang of a Divine Dragon and imbued with the essence, souls, and spiritual power of the twelve Divine Dragons. Combined with the Eye of the Dragon, it transforms into the True Dragon Sword, and can kill supernatural beings and supreme deities.
Genshin (Ninja Gaiden series) wielded the Blade of the Archfiend, a sword rumored to have been forged from a meteorite infused with the Archfiend Vazdah's demonic magic.
Nightmare (Soul series) wields the demonic sword Soul Edge. The sword was once an ordinary weapon until became bathed in the blood and hatred of numerous wars, turning into a powerful demonic weapon with the demonic Inferno as its soul and asborb the souls of other to increase its power.
Siegfried Schtauffen (Soul series) is one of the chosen wielders of Soul Calibur, a holy sword forged by Agol from the purified fragments of Soul Edge and infused with his life-force in order to counter the evil demonic sword.
Xeno Trunks (Super Dragon Ball Heroes) wields the Key Sword, a weapon created by gods to fight and seal demons. Fully charged with the powers of light, darkness, and time by Chronoa, Tokitoki, and Demigra, the sword is able to defeat the fully powered Demon God Mechikabura.
Link (The Legend of Zelda series) wields the Master Sword. The Master Sword is the Blade of Evil's Bane, infused with the sacred flames of the Golden Goddesses and blessed with Hylia’s power in order to strike down even the greatest of evils.