"Aquarium" is a manga series that explores themes of identity, memory, and human connection through a blend of science fiction and psychological drama. The narrative centers around a young man named Sora, who lives in a dystopian future where humanity has been forced to adapt to life underwater due to catastrophic environmental changes on the surface. Society is divided into two distinct groups: the genetically modified "Aquans," who are engineered to thrive underwater, and the unmodified "Landians," who struggle to survive in the submerged world.

Sora, an Aquan, works as a caretaker at an underwater facility that houses preserved memories and consciousnesses of individuals from the surface world. These memories are stored in a vast digital archive known as the Aquarium, which serves as both a historical repository and a source of emotional solace for the isolated underwater population. Sora's role involves interacting with these digitized consciousnesses, helping them reconcile their pasts while grappling with his own fragmented memories and sense of self.

The plot intensifies when Sora encounters a mysterious Landian girl named Aoi, who infiltrates the Aquarium in search of her lost memories. Aoi's presence disrupts the fragile balance of the underwater society, revealing hidden truths about the Aquarium's purpose and the ethical dilemmas surrounding the preservation of human consciousness. As Sora and Aoi form an uneasy alliance, they uncover a conspiracy involving the Aquarium's creators, who have been manipulating memories to control the population and maintain their power.

Throughout the series, the relationship between Sora and Aoi evolves as they navigate the complexities of trust, loss, and the blurred boundaries between reality and memory. Supporting characters, such as Sora's enigmatic colleague Rina and the morally ambiguous scientist Dr. Kuroda, add depth to the narrative, each representing different perspectives on the ethical implications of memory preservation and genetic modification.

The story delves into the psychological impact of living in a world where memories can be altered or erased, raising questions about the nature of identity and the consequences of technological advancement. The underwater setting serves as a metaphor for the characters' emotional isolation and the societal divisions that arise from humanity's attempts to adapt to a changing world. The series concludes with a resolution that balances hope and ambiguity, leaving room for interpretation regarding the future of Sora, Aoi, and the world they inhabit.