This is something I put together essentially because I felt like it. Mechanically, its most obvious feature is taken from the Swords of the Cross- but background-wise, it's got a rather different feel...

I see this as a potential weapon for a PC (and I may play Last Scion of the d'Ortonnes Family sometime myself...), but it could just as easily be the spark for a plot in which the PCs have to find it and take it up temporarily to kill something very nasty, or to return it to safe hands before the bad guys can get hold of it and kill something that really shouldn't be killed.

The d'Ortonnes Sword (Item of Power) [-4 Refresh (base)]

This is a sword steeped in death. It was made to kill that which could not be killed- forged for Sir Joseph d'Ortonnes in the 13th Century to drive off a being of shadow and flame that was terrorising his estate. The sword was made by a robed stranger garbed as a monk, and Sir Joseph paid a terrible price for it- the stranger claimed a weapon suitable to destroy his foe required the sacrifice of seven innocent lives to give it the necessary power. Enough lives had been lost that he agreed, and seven of his peasants were taken by the monk, never to be seen again.

He returned with a sword- elegantly made from bright steel, and yet somehow... harsh. The light reflects cruelly from its edges, drawing attention to the sharp tip. It is quite clearly an instrument of death.

The Sword was passed down the family line from father to son- or daughter, in a few cases, when no sons were available- with a duty to care for it, use it to destroy those that prey on society- and to keep it from the hands of those who would misuse it.

For the d'Ortonnes Sword is a powerful tool, and easy to claim- it will accept a new wielder simply by a mingling of their blood and that of the previous wielder in a pit on the pommel. The family have been forced to fight off numerous assailants who sought it for their own ends, and even reclaimed it after a theft on more than one occasion.

The saddest of these, though, are when it must be taken from one of their own who has been seduced by the power they bear. It is a terrible weight, and one that they bear, for they cannot trust anyone else with it.

Effects:
Demonic Co-Pilot: Applies when the Sword is unsheathed and in use. The sword's spirit's Agenda is quite simple- it was created to kill, and it wants to kill. It doesn't really care what.
The End of Things: The bearer of the d'Ortonnes Sword may pay a fate point to ignore a single target's armour and supernatural protection for the duration of a single scene, as if it satisfied the Catch. [Equivalent to the power of the Swords of the Cross... though not nearly as benevolent.]
It's a Sword: Duh.
Unbreakable: As an Item of Power.
The Power Within: The spirit of the Sword has more to offer- at a price. Over seven centuries of bloodshed, it has amassed a great deal of power, and a willing wielder can allow some of this power in, making him incredibly strong and fast- the better to do the work of the Sword. The wielder may at any time gain Inhuman Strength and/or Speed, immediately modifying his Refresh total and paying two fate points as if using on-the-fly character creation. The wielder must also modify an Aspect to reflect the murderous impulses of the Sword- for example, Guardian Against Darkness might become Uncompromising Slayer of Darkness. The same process may be used to acquire Supernatural or even Mythic Strength and Speed- but the repeated changes to Aspects combined with the high Refresh cost means this is not for the faint-hearted...