"Blue Gender" is a science fiction anime series set in a dystopian future where humanity faces extinction due to an alien species known as the Blue. The story begins with Yuji Kaido, a young man diagnosed with a rare disease, placed in cryogenic sleep in the late 20th century. He awakens over two decades later to find Earth overrun by the Blue, insect-like creatures that have decimated human civilization. The remnants of humanity have retreated to a space station called Second Earth, orbiting the planet.

Yuji is rescued by a military unit known as the Space Cryogenics Tactical Squad, led by the hardened soldier Marlene Angel. The squad's mission is to retrieve cryogenically frozen individuals like Yuji, who are believed to hold the key to humanity's survival. Yuji, initially disoriented and unprepared for the harsh realities of this new world, struggles to adapt to the constant threat of the Blue and the militarized society of Second Earth.

As the narrative progresses, Yuji and Marlene develop a complex relationship, with Yuji's idealism clashing against Marlene's pragmatic and survivalist mindset. The series explores themes of humanity's resilience, the ethics of survival, and the consequences of technological advancement. Yuji's unique condition, which grants him a mysterious connection to the Blue, becomes a focal point of the story, raising questions about the nature of the creatures and humanity's role in their creation.

The plot delves into the political and social dynamics of Second Earth, where a rigid hierarchy and authoritarian rule dominate. The leadership, led by Director General Howe, prioritizes the preservation of the human race at any cost, often resorting to morally questionable methods. Yuji and Marlene's journey uncovers dark secrets about the origins of the Blue and the true intentions of Second Earth's leaders, leading to a climactic confrontation that challenges their understanding of humanity's future.

Throughout the series, the characters grapple with their identities and the moral dilemmas of a world where survival often comes at the expense of compassion. The narrative balances intense action sequences with introspective moments, creating a compelling exploration of human nature in the face of existential threats. "Blue Gender" presents a thought-provoking and emotionally charged story, blending science fiction elements with a focus on character development and ethical questions.