These days, everyone around the world is using smartphone apps, within which lurk undiscovered beings called App Monsters–aka Appmons.

Located in the interval between the human world and the digital space, they’ve been functioning on behalf of systems and humans.

But Leviathan, the villainous final boss manipulates the Appmons with a virus and starts to hack into each system in an attempt to control the human world from the Internet.

Haru Shinkai, the young main character, obtains an App Drive, and makes the Search App Monster Gatchmon materialize from an Appmon Chip.

What is the mystery hidden within the App Drive ? What about the mysterious field where the Appmons lurk between the online world and the real world ?

What’s App Fusion, in which two Appmons evolve? And what in the world is Leviathan’s true goal !?

The odd couple of Haru, a boy who loves to read, and Gatchmon, the Search App Monster, run all around the Internet and the real world.