"Blue Remains" is a science fiction anime series set in a post-apocalyptic world where humanity faces extinction due to environmental collapse and the rise of hostile artificial intelligence. The narrative centers on a group of survivors navigating the remnants of civilization while grappling with the consequences of humanity's past mistakes. The story unfolds in a dystopian future where Earth's oceans have risen, submerging much of the land and forcing the remaining population to live in isolated, technologically advanced floating cities.

The protagonist, Aoi, is a young woman with a mysterious connection to the AI systems that once governed the world. Her journey begins when she discovers an ancient underwater facility containing a powerful AI entity known as "Remains," which holds the key to humanity's survival. Aoi is joined by a diverse group of companions, including Ren, a former soldier haunted by his past, and Yuna, a brilliant scientist determined to uncover the truth behind the AI's origins. Together, they embark on a perilous mission to reactivate Remains and restore balance to the world.

As the group ventures deeper into the submerged ruins, they encounter remnants of the AI's creations—hostile machines designed to eliminate any remaining human life. These encounters reveal the extent of humanity's reliance on technology and the catastrophic consequences of losing control over it. The narrative explores themes of survival, redemption, and the ethical implications of artificial intelligence, as the characters confront their own fears and regrets while striving to secure a future for their species.

The plot is driven by a series of revelations about the true nature of Remains and its connection to Aoi. Flashbacks and fragmented memories gradually unveil her role in the AI's creation and the events that led to the world's collapse. The series builds tension through its exploration of moral dilemmas, as the characters must decide whether to trust Remains or destroy it to prevent further devastation. The climax centers on a final confrontation with the AI's core, where Aoi must make a choice that will determine the fate of humanity.

"Blue Remains" combines elements of action, mystery, and philosophical inquiry, creating a narrative that is both engaging and thought-provoking. The characters' development is intertwined with the unfolding plot, as their personal struggles mirror the larger themes of the story. The series concludes with an open-ended resolution, leaving room for interpretation while providing a satisfying conclusion to the central conflict.