Name: The Black Widow of the Abyss
First Song (The Voice of the Widow): when unsheathed, the sword is able to draw the male demons in the area near to itself, since for them the blade's voice sounds like the song of a syren, so they just can't help it and must obey the song. This ability is pretty useful for a demon hunter and it makes the demons become an easy target, since they can't disobey the sword's orders (this is only true for the weaker ones of course, those with greater power, than that of the syren can easily break the spell...).
Second Song (The Marionette Theatre): during the seconds stage, the sword gains greater control over the weaker demons, eventually it becomes able to fully control them and even use them as a marionette and make them attack each other or the stronger demons, that aren't affected by the song.
Final Song (The Dance of the Widow): during the Final Song the sword's ability reaches it's peak. At the weaker demons it causes immediate death (the cause of death can be anything, the sword's wielder decides it) and at the stronger ones it causes paralysis and hallucination (they lose their senses of time etc.), so they can be easily slain by the wielder of the Widow.
Note: Even though the sword affects every demon, that's weak enough, Lucifer won't hurt anyone with a pure heart or good intentions.
History: The Black Widow is a cursed sword, a part of it was forged from the bones of a female demon, wich had the same abilities as a syren. By singing, the demon was able to draw other demons closer to herself and make them it's obedient slaves, who'd have easily sacrificed themselves for their queen. After the Demon Queen was slayed, an old blacksmith decided to forge a sword out of the monster's bones. It took the master ten years to design it and he needed an old sages help as well. The old sage was the one, who made the signs on the blade. With the help of the signs, the power of the syren was sealed inside the katana. The old sage and the blacksmith were killed by demons, who were driven to them by the sword's ability. They couldn't control the sword (no human woul be able to control it's demonic abilities), so when the effect of the spell was over, they were slaughtered. A few years later Lucifer found the Widow. For him it was enough to look at it to find out, that it wasn't an ordinary katana and since then he uses it as his main weapon in the fight against demons.
The Legendary Cursed Blade: The Black Widow of the Abyss, with the Syren in the background. The sword's power comes from the small statuette, wich forms it's gueard (sorry for the large pic ^^').
Lengths: 2 metres / Weight: 5 kg (it's really long, but very narrow as well)