Imitar is a black void that was a sentient piece of Chaos itself. He broke away from Chaos when Galaxia seald Chaos within herself during the Sailor Wars. He has the ability to shapeshift into any thing he sees. The Metallic Guards were once Senshi (OK, only Maeve since Senshi can only be female. The other two were guards like Tuxedo Kamen-sama), whose Starseeds were taken and turned evil by him.
Shizar is the leader of the Metallic Guard. His armor is golden, as is his hair and eyes. Unlike the other two, he is mostly spell dependent and uses minions to do his bidding. i.e. Stormfire.
Maeve is the lieutenant of the Metallic Guard. Her armor is all silver, as her hair and eyes. She is the most dependable, or so Imitar thinks, of the group. She was secretly in love with Shizar, who was killed by Imitar. After Shizar's 'death' she goes on a rampage, trying to kill Sailor Earth.
Valtork is the underdog of the Metallic Guard. His armor is all bronze, as his hair and eyes. He is the most disliked of the group. Even Imitar really doesn't trust him. He rats on Shizar and Maeve out about their secret relationship only to take over Shizar or Maeve's position.
Nova is the sister to Sailor Galaxia-sama. Like Galaxia's duty to guard the galaxy, Nova's was to guard the stars. When Galaxia trapped Chaos within herself, Nova witnessed a change that overcame her sister. Unlike Galaxia, who was actually GOOD at first, Nova was a total monster her entire life. It was only Galaxia's kindness and love that kept the monstorus Nova in check. During the Sailor Wars, Galaxia and Nova became separated. While Nova was in another solar system, destroying every planet she crossed because she was searching for her sister, she heard a rumor that Galaxia was killed, not healed, by Eternal Sailormoon. She came to earth with hopes of destroying Moon, but Earth got in the way. Now she's after Earth and Moon with hopes of destroying everything.
Brimstone is the Senshi of fire and brimstone, albeit she's not that bright. Her entire body, including clothing, is red. Her hair is actually a burning fire.
Adonia is the armored Senshi of beauty. She has long white hair and icy blue eyes. SuperSailor Uranus smacks her around. I mean, who else deserves to get slapped around a bit?
Titanium is the armored Senshi of steel. She has steel gray eyes and hair. She's the strongest of the three; she even manages to escape barely. She also carries over into The Utopian Chronicles There are plans for Titanium to appear later as a normal civilian.