Christella Revi

Christella Revi is the main antagonist of the series and the one Birdy is trying to capture, a prodigy turned terrorist, it is revealed in the reboot manga that Revi seeks to liberate the oppressed Altans of the Space Federation and will use any means to do so. She is usually accompanied by Gomez and several marionettes who protect her from all harm.

Decode
In Decode, the Federation is not aware Revi is hiding on Earth, she most likely had some contact with Shyamalan and lent him Undine to help him execute his mission, additionally she seems to have known Geega through Gomez and was aware of the Ryunka's destructive powers however she did not wish for it to kill so many people. In the 4th episode of the second season, Revi is briefly mentioned as having joined up with the higher ups of East Delta, she is also said to have risen through the ranks of the federation with her great scientific knowledge and standing up for the rights of Altans. During the Central Tower Attack, Revi mocks the Federation for their inability to prevent her from committing another attack after the one at Akrabal two years prior, she explains how she pondered whether the Federation would listen to her if she was to attack Oriotera instead and says she has gained the support of the Altan Liberation Front, East Delta. As part of her demands, she demands the independence of the planet Alta from the Federation.

Decode
Revi is most likely the person talking to Gomez on the phone during the end of the ninth episode, she later makes her first appearance in the beginning of the tenth episode, though her appearance and name are not revealed, she is informed by Gomez that Shyamalan is incapable of properly handling his mission, Revi wishes to see the darkness within him. During the ending of the 13th episode of the first season, Revi makes her first and only appearance in Decode, as Gomez and her observe Birdy hopping on the rooftops, Gomez informs Revi that Birdy does not possess any threat towards their plans but that she has good senses, Revi expresses interest in response.

In the 4th episode of the second season, Dusk mentions Revi in a flashback, she is later mentioned and heard again in the 7th episode where during his memory dive, Tsutomu experiences Birdy's memories of the Central Tower Attack, while it is happening, Revi announces her intentions and demands from the Federation. In the 11th episode, Gomez mentions that Revi has decided to break the agreement between her and the fugitives due to their carelessness in handling the Ryunka, Moss threatens Gomez that she will report Revi's hideout on Earth to the Federation and in return Gomez mocks her and tells her that she may do as she pleases and leaves.

It's never made clear whether Birdy even knows about Revi's existence or not as she never mentions her name nor reacts to it.

Abilities
Prior to his fusion with Tunica, Revi was a fairly average Altan who did not possess any real abilities, however after the fusion, Revi gained some of Tunica's attributes.

Intelligence: thanks to Tunica, Revi is incredibly intelligent, able to remember countless religious and historical documents, analyze the situation to an extreme precision and always have a plan.

Transformation: albeit not under control, after the fusion, Revi's body would at times of trouble, transform into a female one, Revi only has partial control over this ability as she can predict when it will occur but cannot access it at will like other Ixorians.