After all this time, here's updated information about the InfraRed cast in (approximate) order of appearance.

Infra
Race: Demon
Abilities: Pyrokinesis - Fire manipulation. At first he merely has control over his own fire, but gradually gains the ability to take control of fire produced by other means. He also learns how to take on a new form in which he is entirely made of flame.
Alignment: Various
Background: Infra was once one of Lucifer's peons, but was dismissed by the tyrant. Infra swore revenge on his betrayer and since then fights whatever evil Lucifer brings to Earth.

Lucifer
Race: Demon (originally Angel)
Abilities: Dark force manipulation - Demonic energy attacks.
Soul manipulation - Lucifer can mould the souls of people that have been condemned to Hell into other beings, such as demon soldiers. He can mould multiple souls into one massive being such as a Leviathan, or even divide souls to make lesser creatures like Wavers.
Alignment: Evil
Background: Once an angel of Heaven, Lucifer was thrown to Earth where he dug into the ground and hollowed out Hell. Originally content with opposing everything Heaven stood for and claiming souls, Lucifer became corrupted by the power as Lord of Hell and so he built up an army and announced his campaign to enslave humanity and work his way up to Heaven. After an incident involving Vanity and Chastity, Lucifer was sealed in an underground chamber by Edward the second Lord of Heaven. From this chamber he is still able to command his peons, but cannot go into battle himself. His goal remains the same.

Ultra
Race: Angel
Abilities: Water manipulation - Unlike Infra's primarily fighting-based fire, Ultra's element manifests in many ways. He can fire waterbombs at enemies and shield himself in a durable bubble. Later he is taught how to cool his water skill and learns to manipulate ice.
Healing - Minor healing ability, allowing Ultra to seal small cuts and remove bruising.
Alignment: Good
Background: Ultra has spent his life working for Heaven. After Lucifer's betrayal of Infra he was the only one to accept and support his brother despite past disputes between the two.

Tempo
Race: Android
Abilities: Plasmoid blasts - Small balls of green plasmoid energy that are fired from Tempo's right arm.
Homing rockets - Small rockets that are fired from Tempo's left arm and home in on her target.
Alignment: Good
Background: Tempo was created as the final product of an AI project by Dr Matt Gladman and his wife Midori. Gladman continued the project even after the death of his wife and named it "Tempo" as a tribute to her love of music. However, Gladman was forced by the police to convert Tempo into a fighting machine capable of destroying Infra.

Guile
Race: Angel
Abilities: Cloning - Guile was a scientist on Earth, and has kept his knowledge and experience after death.
Alignment: Various
Background: Guile was one of the most work-oriented angels in Heaven and was the definite favourite of Henry, third Lord of Heaven. However Henry began favouring Ultra upon his arrival due to his unusual creation. Guile understandably became envious and grew hostile toward Ultra. When Ultra was promoted to High Seraph, a position that Guile had been a shoe-in for, it was the final straw and Guile plotted to kill both Ultra and Infra, with the help of...

Supra
Race: Demon
Abilities: Electrical manipulation - Like Infra, Supra mainly uses his element for fighting, such as with lightning punches and balls of energy. The other way he can attack is by forming a long whip out of electricity that protrudes from his hand. The end of this whip will latch on to Supra's target so he can pull enemies closer to him. He can also use it to latch onto a building and pull himself up.
Alignment: Various
Background: Guile created Supra using a sample of Infra's blood. Supra went after Ultra as he had been ordered, but once noticing his own resemblance to Infra, turned on Infra instead to prove he was a superior being. He had the upper hand until Ultra attacked him, revealing he had inherited Infra's water intolerance. Infra tricked him into falling into the ocean, where he (seemingly) died.

Abhor
Race: Reaper
Abilities: Soul harvesting - Abhor always has his scythe handy. By channeling magic into it and turning the blade green, he can kill a being with just one touch. Being a sharp bladed instrument it can naturally be used for fighting as well.
Alignment: Evil
Background: While most Reapers worked for the Grim One, harvesting only the souls that were ready to leave Earth, Abhor grew to love his work too much and was ejected from the Death Syndicate for unauthorised harvesting. He turned to Lucifer who promised him plenty of work.

More to come.