Marlene Angel is the main heroine of Blue Gender: The Warrior. Orphaned at the age of ten after her parents were killed by the Blue, she was among the few survivors who made it to Second Earth, a space station where the remnants of humanity have taken refuge. From that point, she dedicated herself wholly to defeating the Blue, undergoing intense and brutal training throughout her childhood and adolescence. This upbringing stripped her of many conventional feminine traits and left her emotionally underdeveloped; she initially has little understanding of the differences between men and women, and she appears cold, heartless, and purely mission-focused.

Her primary motivation is revenge against the Blue, which she channels into serving as a soldier. She is highly disciplined, practical, and by-the-book, viewing her duty as the only meaningful purpose. When she is assigned to lead a Sleeper Recovery Team tasked with retrieving cryogenically frozen individuals from the surface, she initially regards the civilian Yuji Kaido as nothing more than cargo. Her role in the story is that of a hardened warrior who gradually rediscovers her humanity through her journey with Yuji. Over time, she begins to experience emotions she had long suppressed, and the bond that develops between them softens her sharp edges. They become romantically involved, and Marlene evolves from a stoic soldier into a passionate protector who is willing to rebel against Second Earth's High Council to find and help Yuji when he is taken away.

Key relationships include that with Yuji Kaido, who serves as the catalyst for her emotional awakening. She also interacts with other soldiers on the team, but most perish during the mission, leaving her isolated with Yuji. Her development is marked by her initial inability to relate to Yuji or understand his civilian perspective, followed by a growing empathy and eventually a deep love that leads her to fight not just for revenge but for his sake. By the end of the story, she is pregnant with their child, symbolizing her full reintegration of humanity and hope.

Notable abilities include elite-level combat skills honed through years of vicious training. She is a first-class pilot of the Sniper class Armored Shrike, a mecha used against the Blue. She is resourceful, resilient, and physically capable, able to survive prolonged ground missions and face the Blue in direct combat. Her mental toughness allows her to suppress fear and doubt, but her greatest strength may be her will to reconnect with her own heart and to pull Yuji back from the brink of madness when his own powers threaten to consume him.