This is a theme based on the Pokemon games, with elements of the anime. The world of Pokemon is filled with the creatures known as Pokemon, a vast variety of different species of collectible combat creatures. Humans known as Pokemon Trainers head out to the wild, capturing Pokemon in Pokeballs, and using them in battle. Pokemon are also sapient species, capable of communicating, and generally willing to pair up with humans who are skilled enough to capture them.
Various villainous organizations are trying to use Pokemon for their own purposes. Team Rocket uses Pokemon for profit. Team Aqua and Magma want to increase the size of the sea, or the size of the land, respectively. Team Galactic seeks to completely remake the world. Team Plasma seeks to liberate Pokemon from their slavery to humans. Team Flare seeks to end most life.
But, each of these organizations faces fierce opposition. Various Gym Leaders stand against them, as do some members of the legendary Elite Four. What is more, there are some heroic trainers, setting out on their journeys to become Pokemon Masters. These new trainers are often some of the greatest threats to these villainous organizations.