They were born as Adira on Earth in 3173. (DIS: "People of Earth") Adira lost their parents at a young age, becoming an orphan. In the 3180s, Adira was abord a generation ship seeking out Federation headquarters. They formed a relationship with Gray, a young Trill. Following the death of Admiral Senna Tal, who was also aboard, Gray was joined with the Tal symbiont. He reassured Adira that this would not change their relationship.
In 3188, the ship was struck by an asteroid, killing Gray and wounding Adira. With Adira's consent, medical drones implanted the Tal symbiont in Adira, the first successful joining with a non-Trill in 2,000 years. Adira escaped the ship in an escape pod, where they were found by the United Earth Defense Force. They lost their memory up to that point. (DIS: "Forget Me Not")
United Earth Defense Force service
In 3189, Adira participated in the Defense Force inspection of the USS Discovery. While investigating the engineering section, they showed their technical acumen by quickly noticing several facts about the ship's technology. Fascinated by the by-then-ancient technology as well as the spore drive, they sabotaged Discovery's systems to interfere with the Defense Force inspectors' personal transporters, then struck out independently to investigate the ship.
Adira's search led to a confrontation with Paul Stamets in a Jefferies tube. The two struck up a friendly conversation, and they asked and were allowed to join the crew of the Discovery. They also revealed that Admiral Tal, for whom Discovery was searching, was actually Adira themself: despite being Human, they had become the host to the Trill symbiont Tal after their boyfriend Gray Tal's death. (DIS: "People of Earth")
When the Discovery approached Federation Headquarters, they, along with Captain Saru and Michael Burnham, met with Fleet Admiral Charles Vance, the commander-in-chief of Starfleet. (DIS: "Die Trying")
When the Discovery underwent a retrofit with 32nd century technology, Adira changed the spore drive interface to utilize nanogel, allowing Stamets to control the spore drive without needing to use his implants, allowing them to be removed. (DIS: "Scavengers")
By analyzing the combined data from several black boxes, and the SB-19 data from Ni'Var President T'Rina, Tal and Stamets were able to pinpoint The Burn's point of origin. They were also able to identify a signal which was still being sent as a Federation distress call. Adira then wrote an algorithm to decode this message.
After becoming more comfortable with Stamets, Adira told him, "I've never felt like a 'she' or– or a 'her,' so… I would prefer 'they' or 'them'." Stamets was the first person Adira had told besides Gray. (DIS: "The Sanctuary")
When Saru, Hugh Culber, and Michael Burnham were trapped on Theta Zeta in the Verubin Nebula and at risk of deadly radiation exposure, Adira concealed themself aboard Booker's ship without the crew's knowledge, and beamed down to the planet with radiation pills to buy the away team some time. (DIS: "Su'Kal") The holographic environment aboard the KSF Khi'eth caused them to look like a Xahean and also made Gray appear in the form of a Vulcan hologram. (DIS: "That Hope Is You, Part 2")
Following the rescue of Su'Kal from the wreckage of the Khi'eth and the defeat of Emerald Chain in 3189, Adira was given a Starfleet commission as an ensign in the sciences division. (DIS: "That Hope Is You, Part 2")
|The hosts of Tal|
|Kasha • Jovar • Madela • Cara • Senna • Gray • Adira|
Adira is played by Blu del Barrio and is the first recurring character in the franchise not to identify with their assigned gender at birth.
Adira's non-binary identity was discussed on both StarTrek.com and in a GLAAD interview stating that, like del Barrio, Adira is recognized as non-binary and uses they/them pronouns. Blu del Barrio said, "They remember nothing from their past, and very little about themself. They know they're non-binary, of course, but coming onto Discovery they're cautious about sharing that information with anyone… It's not until Adira has found a place of comfort with Stamets and Culber that they feel they can talk about who they are."   Because of this, both Adira and other characters consistently used feminine pronouns in the episodes in which the character appeared prior to "The Sanctuary". As part of the publicity around the introduction of Adira, del Barrio made it clear that Adira's non-binary identity would have nothing to do with their being joined with a Trill symbiont. 
Del Barrio commented: "To research for the role of Adira, I watched Star Trek: Deep Space Nine. Specifically, to follow the storyline of Jadzia Dax (now one of my favorite characters). There's not a whole lot of information about the Trill species elsewhere in the other series, so I spent a lot of time with DS9".