"Aquatic" is set in a futuristic world where humanity has adapted to life underwater due to the catastrophic flooding of Earth's surface. The narrative centers on a young marine biologist, Kaito, who works for the Oceanic Research Institute, an organization dedicated to preserving the fragile balance of the underwater ecosystem. Kaito's life takes a dramatic turn when he discovers a mysterious, sentient aquatic creature named Luma, which possesses the ability to communicate with humans and exhibits unique powers that could either save or destroy the underwater civilization.

As Kaito and Luma form an unlikely bond, they uncover a conspiracy orchestrated by a powerful corporation, Nereus Industries, which seeks to exploit Luma's abilities for profit and control over the oceanic resources. The corporation's experiments threaten to destabilize the delicate harmony of the underwater world, leading to environmental collapse. Kaito, alongside a group of allies including his childhood friend and engineer, Aya, and a rogue former Nereus scientist, Dr. Ren, embarks on a mission to protect Luma and prevent the corporation's destructive plans.

The series explores themes of environmentalism, the ethical implications of scientific advancement, and the coexistence of humans and nature. The plot unfolds through a series of escalating conflicts, including underwater battles, political intrigue, and moral dilemmas, as Kaito and his team navigate the challenges of their mission. The characters are developed through their interactions and personal struggles, with Kaito's growth from a reserved scientist to a determined leader serving as a central arc. The story culminates in a climactic confrontation with Nereus Industries, where the fate of the underwater world hangs in the balance.