Marlene Karn was the first daughter of Zeon admiral Maharaja Karn. Her beauty had caught the eye of Vice Admiral Dozle Zabi, and she was subsequently taken as his mistress. This was also done to garner protection for the Karn family, whose head, Maharaja Karn, was a survivor of the political purge of Pro-Zeon Zum Deikun loyalists enacted by the ruling Zabi's. In turn, Maharaja was appointed as the regent on the newly-discovered Axis, away from the political infighting in Side 3. While her father was stricken by feelings of guilt as a result of this, Marlene however is treated courteously by Dozle, and often accompanied his wife Zenna Zabi as an attendant.
As the One Year War drew to a close, Marlene fled the Earth Sphere, immediately before the fall of the Zabi family, in obedience to Dozle's wishes. Marlene had always been physically weak. Her younger sibling, Haman Karn, had attempted to prevent her from leaving, due to her weak health. Sympathizing with Marlene's wishes, Haman left the Earth Sphere along with their youngest sister Serrana Karn and father, but still resented Marlene for doing so. Marlene died before reaching the asteroid belt, and Haman became one of Mineva Lao Zabi's attendants in her sister's place.