Orphaned at the age of ten because her parents were killed by the Blue, Marlene was one of the few lucky ones to make it to Second Earth. Since then Marlene has dedicated and trained herself to defeat the Blue, taking all kind of vicious training during her early days making her lack of many female atitudes.

She doesn't understand the difference between a woman and a man, making it difficult for Yuji to deal with her. Though seeming very cold in the earlier episodes, as time progresses, Yuji opens up Marlene's emotions.