Karla Mitchum is a professor and scientist who served the Principality of Zeon during the One Year War, primarily aboard the flagship Dried Fish as part of the Living Dead Division. Her expertise lies in the field of prosthetics and biological interfaces, making her a central figure in the development of the Reuse P Device system, which was designed to improve the synchronization between amputee pilots and their mobile suits. Beyond her research, she was also entrusted with performing the prosthetic surgeries on the wounded soldiers of the division. Her service to the Zeon military, however, was not born out of ideology but from a deeply personal motivation: she was forced to cooperate with the war effort to save the life of her father, a historian who had been imprisoned as a political dissident by the Zeon regime.

In her role within the Living Dead Division, Karla formed significant personal bonds that drive much of her character arc. She was romantically involved with Ensign Hoover, the unit's initial mobile suit team commander. His death at the hands of the Earth Federation pilot Io Fleming was a devastating blow that shattered Karla and ignited a fierce desire for vengeance. She subsequently tasked the ace pilot Daryl Lorenz with killing Io, marking the beginning of a complex and evolving relationship with him. As Daryl continued to lose limbs in combat against the Gundam, Karla was forced to perform further amputations to increase his compatibility with the experimental Psycho Zaku, a process she initially resisted but accepted to save her father. Through this shared trauma and dependence, their professional relationship deepened into romantic feelings, culminating in a shared kiss before Daryl’s final sortie, during which he declared her his reason for living.

Karla was present on the Dried Fish during the final Federation assault in the Thunderbolt Sector. During the battle, she manned a gun turret in a desperate attempt to fend off the enemy. When the ship was crippled, she and her fellow scientists prepared charges to scuttle it. As a colleague pleaded for calm to prevent further bloodshed, Federation forces pinpointed their location and attacked. Karla noticed the targeting camera and attempted to stop the impending strike, but was too late; a Federation mobile suit used a beam saber to vaporize her entire team. Witnessing this atrocity sent her into a catatonic state, and she remained unconscious until after the war had ended.

The psychological trauma Karla endured had a profound and permanent effect. Upon waking, her mind regressed to that of an adolescent, and she failed to recognize Daryl as her partner, instead identifying him as her papa. In this state, she came under the care of a Zeon medical team aboard a submerged Dolos-class ship operated by Zeon remnants, with Daryl continuing to visit and care for her as she slowly recovered from the level of an infant to that of an elementary school child. Beyond this extreme trauma, Karla is characterized as someone who deeply cares for the soldiers around her and displays little desire for personal accolades, such as the Zeon Science Medal she was once awarded. Beneath her service, she also harbored a deep-seated resentment towards the factions that used her work, a bitterness that would later drive her to extreme actions in the post-war period, such as firing a colony laser.