The protagonist of the story is a young male blue-ringed octopus named "Sapphire". He is full of curiosity and is not satisfied with the comfortable life in Coral City. He dreams of exploring the legendary "Spine of the World" mountain range and the "Eternal Wind" Sky City. In an accident, he inherited the memory fragments of the ancient "intelligent whale" and learned that an ancient covenant related to the balance of the three realms was disintegrating, and a huge disaster "The Great Annihilation" was about to happen again. In order to find the truth and prevent the disaster, Sapphire and his three friends - from the land (the raccoon "Spirit Claw"), the sky (the peregrine falcon "Wind Roar") and the ocean (the humpback whale "Song") - formed an adventure group that spanned three realms, from the blazing underwater volcano to the cold cloud city, solving ancient mysteries one after another, and finally revealing the grand secret of the evolution of life.
