Katsura Mafune was the daughter of Dr. Shinji Mafune. As a young girl she developed a close relationship with her father's discovered dinosaur, Titanosaurus, whom she could control. When she was a young girl helping her father in his laboratory she suffered an accident that almost killed her. However Dr. Mafune's benefactor, a man named Tsuda, had her taken away to an operating room where his surgeons saved her life by replacing her internal organs with mechanical ones, turning Katsura into a cyborg. Thereafter, Mafune began training his daughter to start using Titanosaurus as an instrument of revenge.
Unknown to Mafune, Tsuda held sway over Katsura due to the origins of her cybernetic components, and was able to make her serve the Black Hole aliens, then led by Kuronuma, behind her father's back. After Kuronuma's death and the destruction of Mechagodzilla, Tsuda had Katsura use Titanosaurus to keep Interpol submarines away from where the wreck of Mechagodzilla fell off of Okinawa, allowing his men to salvage the robotic monster in preparation for the arrival of Kuronuma's replacement, Mugaru.
When Interpol came to Manazura Island looking for Dr. Mafune, Katsura met and took a liking to the young marine biologist Akira Ichinose. They two began dating (despite the objections of Mafune, who had his butler follow them everywhere). Katsura's time with Akira made her begin to question her father's bleak outlook on the world, and she wanted his quest for revenge to end. However Mafune reminded Katsura of how her mother had died as an indirect result of society shunning them, which re-ignited her sense of duty both to her father and her late mother.
When Interpol developed a sonic weapon to use against Titanosaurus, Katsura, along with her father's butler, sabotaged the device. They were chased by Jiro Murakoshi and some Interpol agents, and Katsura was shot. The aliens were able to fix her once again, but this time, Tsuda, at Mugaru's instruction, placed the control mechanism for Mechagodzilla inside of Katsura. Eventually, she decided to turn against the aliens. Her father sided with her rather than them, but in an attack upon the Mafune mansion by Interpol, Katsura was wounded by gunfire and her father killed when Mugaru used him as a human shield.
Katsura was reunited with Akira, who had been held prisoner by the aliens but escaped. He told her he loved her even though she was a cyborg, but Katsura told him that the only way for Godzilla to destroy the new and improved Mechagodzilla was for the controller to be destroyed. She then shot herself with one of the aliens' rayguns, killing herself and taking the Mechagodzilla controller with her.