Black Sword

The Black Sword, less frequently known as the Shade Blade, is found in The Forge of Virtue. The Black Sword is the most powerful magical weapon in the game. It is quite obviously inspired by Stormbringer from Michael Moorcock's stories.

There is also a weapon called The Black Sword in the Apple Macintosh[shareware game Shadow Keep. It is the Evil Overlord's former weapon, lost by him during The Great Battle. The wounds it afflicts cannot be healed, "neither by nature nor by magic", and it cannot rust. Sword wielded by Dracule Mihawk in the One Piece manga is also called "The Black Sword". Except for their names, neither bears relation to the sword in the Ultima series.

Description and abilities
The Black Sword is an enchanted two-handed sword. Its blade is made of Blackrock, a magically inpenetratable material. Blackrock is not very easy to shape, therefore powerful magical enhancements are required to make the weapon properly cut and balanced. The most important of these is a magical soul gem embedded to the hilt.

In Ultima VII, the Black Sword is magically bound to the Avatar, and cannot be unequipped. When the sword is activated in the game by double-clicking it, the Avatar is able to converse with the demon Arcadion, who is able to either instantly and noiselessly kill a creature, fill up the Avatar's mana or create a fire field. Arcadion can kill creatures that are very powerful, and refuses to kill creatures that are far too easy to kill in conventional means. Some creatures, he can't kill, like Liches and Stone Harpies. Using the Black Sword is one of the few non-easter egg ways to kill Lord British. Killing Batlin with it is not possible, however.

The Avatar obtains the sword in Forge of Virtue
When the Avatar arrived to the Isle of Firein, he was faced with three tests: the tests of Truth, Love, and Courage.

The final test of Courage was more difficult than the first two, mostly because in order to finish it, the Avatar had to kill a dragon that was practically invincible and capable of reincarnation. However, when he first killed the dragon, he was able to retrieve a stolen magical gem from the dragon's maw.

In the Isle of Fire fortress, the Avatar had met Erethian, an apparently blind man who had come to the island to research many of the papers dating back to the era of Exodus. There, he also met a demon called Arcadion, trapped in a mirror and bound to serve Erethian. Using the gem, the Avatar shattered the mirror, but instead of freeing Arcadion as intended, he only got transferred to the gem.

Erethian then proceeded to help the Avatar by letting him finish a magical weapon he had never finished himself, a sword made out of blackrock. It was then found out that the sword needed the soul gem to get properly balanced. Arcadion, since he was now bound to serve the Avatar, volunteered for that.

Separation and reunion in Serpent Isle
The Black sword didn't appear in Ultima Underworld II, why, isn't clear. In Ultima VII/2, the Avatar and the sword became separated due to the teleport storms that ravaged the Serpent Isle. When the Avatar finally found the sword again, Arcadion had already grown quite rebellious. Finally, in exchange for his freedom, Arcadion agreed to help the Avatar one last time to escape a difficult situation.

Without Arcadion balancing the sword, it became far less potent. The Avatar had to fix it using a flux analyzer, since the sword was the only weapon capable of killing and imprisoning the Chaos Banes inside soul prisms.

Aftermath
The ultimate fate of the sword was not discussed in the last two parts of the game series. It is clear that the sword itself either remained in the Serpent Isle, or vanished with the Avatar to the Ethereal Void in the end of Ultima VII/2. When looking at the file that contains all the text of Ultima VII though, you can see a conversation between the avatar and the blacksmith on Pagan about constructing a sword made of blackrock. It is not possible to discuss this with the blacksmith in the game, but it might mean that the original plans was to include it either in the main game or the add-on that never got released, The Lost Vale.

Arcadion's later whereabouts are unknown. In Ultima VIII, The Avatar did meet Arcadion one more time, on the world of Pagan. However the demon claimed not to recognise the Avatar, nor did it remember anything about being trapped in a sword. It seems likely that the Arcadion the Avatar met on Pagan was the demon before he was trapped by Erethian. This is possible due to the fact that time supposedly moved at different paces between worlds. This explains why the Avatar is always young as he travels between many worlds quite often while the natives are always different. It also explains why the Avatar's friends such as Dupre, Lord British, and Iolo all seem to live for such a long time.