Salacia: Waga Hakugin no Mermaid

In the year 2071, the ice caps of the North Pole have completely melted, plunging the world's landmasses beneath the rising seas. While humanity has managed to survive this global catastrophe, it has fractured into two distinct factions. True humans reside within the safety of enclosed underwater cities, while a divergent group known as the Dugons chose to undergo radical genetic modification to adapt directly to ocean life. The fragile coexistence between the two species shatters when the Dugons begin viewing unmodified humans as prey, igniting a desperate war for survival in the depths. To defend against the relentless Dugon threat, the underwater city of Mari Ramelle engineers a revolutionary weapon: Salacia, an advanced mermaid robot. Because the mecha's pilot cabin is exceptionally compact, it requires two thirteen-year-old operators, Marin Yuuki and Ushio Mizushiro, to synchronize their efforts and control the machine. As the brutal conflict escalates and the struggle for humanity's future grows increasingly dire, the city is forced to construct additional mermaid robots to bolster its defenses against the terrifying predators of the deep.