UESP
The Sword of the Moon Reiver (also known as the Broadsword of the Moon Reiver or Moon-Cursed Blade) is a broadsword created from Mehrunes Dagon’s own substance. It is believed that no other weapon is capable of harming Mehrunes Dagon. During Dagon’s invasion of the Battlespire during the Imperial Simulacrum, the sword was in the possession of his Dark Seducer bodyguard and paramour. An apprentice took the sword from her and used it to banish the Prince from his own realm, resulting in the destruction of the Battlespire.
Modded
In the possession of Master Aryon. According to a Letter from Master Fyr, the sword was a gift from Divayth Fyr.1