Unit #024 is a development-model Anti-Shadow android being used for research and development of the fifth generation of such robots, and appears during the storyline of Persona 4 Arena. Her "name" comes from her being the twenty-fourth such prototype unit produced. Like the other prototypes of the same design, she has been outfitted with a special component called a Plume of Dusk that would allow her to develop an ego, and eventually a Persona. During the research process, she meets Unit #031 during the evening period in which the androids are allowed to roam the exterior grounds of the facility and develop their cognitive abilities. By the time that #031 meets her, #024 has already shown significant signs of progress in this regard. She is friendly toward the newer unit, and each night, they meet with each other to exchange pleasantries that grow more and more sophisticated as #031's own mind and heart develop. The two eventually begin to think of each other as friends.
After the preliminary combat exercises are brought to an end and #031 is both chosen to become the prototype and rechristened "Labrys," #024 uploads a special file in secret to her, to only be opened when everything is over. The next day, Labrys is informed to her horror that she being put through a new series of exercises, and she must destroy the remaining, unchosen prototypes. Her first adversary is none other than #024. Though Labrys doesn't want to fight her, #024 does not have a choice, and goes on the attack, forcing Labrys to defend herself. In the end, Labrys destroys her friend.
When Labrys begins mounting strong protests against the research staff, they lock her up and the data from #024 is uploaded into her. Among #024's memories are a girl with a distinctive Kansai accent that is bed-ridden in a hospital, who had elected to donate herself to research. This girl, the person that #024 so wished to meet, was the figure that she considered her mother, as she was used as the basis for the development of the Generation 5 test series.
As the staff is distracted by their glee, Labrys accesses the secret file that #024 had passed her and finds one last message from her, asking that Labrys not blame herself for #024's destruction, or for the destruction of the others, and that she be happy, just as their mother wished for them to be. This final message from #024 causes Labrys to start crying, and the staff, who do not wish for her to be sentimental, tries to forcibly delete her memories and by extension, those of #024. Refusing to allow this, Labrys goes berserk and destroys the lab before finally being recaptured.
Many years later, an unknown party deposits Labrys in the TV world, where her Shadow concocts the P-1 Grand Prix. This tournament is based on the anguish that Labrys felt at being forced to destroy #024 and the others while the research staff treated them all as little more than lab rats.