Deia is a character who appears in XIII and turns out to be the pivotal protagonist.
After some of his comments cause Deunan to go on a drinking binge, she meets Deia at Hitomi's house, who informs her that Deia is a scientist specialising in the study of Bioroids, working for Poseidon.
Deia then introduces herself by her full name, Deia Chades.
It turns out that Deia was married to Alcides, leader of a once thriving shipborne society called the Argonauts. However, a bioroid clone of her husband leads her into an uncontrollable secret jealousy, and she eventually brings about the death of her husband by giving away the location of the Argonauts' ship to her native Poseidon, allowing them to launch a missile attack. The attack kills her husband, but he dies protecting Deia. The guilt drives her utterly insane.
Deia secretly pilots a giant Hecatonchires-type Landmate and commits several acts of terrorism against Olympus. Her motive is to cause the failure of Olympus' so-called utopia, especially by means of foiling a project to enable humanity to make the first steps towards living in space. This involves bringing about the deaths of all remaining 'unprocessed' bioroids who bear Alcides' genes.
Ultimately, at the moment when Deia is poised to kill the last bearer of these genes, a newborn baby, she finds the clarity of mind to stop. She finds her salvation by means of self-immolation.
- In the English dub, Deia is voiced by Monica Rial.