Now, everyone in the world uses smartphone apps. There lurks an unknown existence, Applimonster, commonly known as "Appmon". Appmon is an App life form with artificial intelligence that can think and act independently. It functions for the system and humans in the gap between the human world and the digital space. However, the "evil final boss artificial intelligence Leviathan" hidden in the sea of network has transformed into a virus to control the Appmons and began to hack into various systems, trying to control the human world from the network side. The protagonist, the boy Haru Shinkai, obtained the "App Driver" guided by the great will and materialized the search app GATCHIMON from the "App Chip". The mystery hidden in the "App Driver", the mysterious "field" between the network world where Appmon hides and the real world, and what is the "App Fusion" that two Appmon evolve from? What is the real goal of "Leviathan"...! ? The book-loving boy Haru and the monster GATCHIMON who search for apps are a pair of convex and concave combinations running in the modern world. The new feeling partner story starts now!