Devour and Evolve

Apocalyptic floods engulf the world, and mutated sea creatures prey on humans. SS Rank esper Victor Bennett is betrayed and killed by his vice captain Tyler Barton, then is reborn as a dying little carp. At the brink of death, he awakens a Devour and Evolution System, inherits the bloodline of the ancient Cosmic Fish, and evolves at an astonishing pace by devouring monsters. Along the way, he rescues investigator Ava Goodwin, reunites with his loyal teammate Neil Carter, and joins forces with them to expose the mastermind behind the apocalypse. He rises from a helpless fish to an SSS Rank Cosmic Fish and becomes the supreme ruler of the deep sea. When the floodwaters recede, Victor returns in his human form and rebuilds human civilization with his companions while protecting the new world.