Quoted By:
"Rodeo" is literally the name of the region the game was set in and also the name of the main island surrounded by other 5 islands (jungle, fire, ice, ruins and forest).
The MCs is a boy/girl aspiring to become a legendary pokemon rider. The reason the pokemon go crazy (called "out of control pokemon" in the documents) is ether particles. "Out of control pokemon" are 3-times bigger and much more feracious than usual. After defeating one of these you get ether particles and turn them into paint to customize your ride pokemon.
There's actual lore on the Rodeo region too:
>Rodeo has suffered plenty of natural disasters in the past and it's said that rampaging pokemon were the reason.
>1000 years ago, a legendary pokemon rider and his special pokemon calmed the rampaging beasts.
>The way people and pokemon worked together to prevent this crisis was made into a legend that is talked about to this day.
Aside from the raid bosses they planned quests like catching a Charizard, killing 100 Magikarps or collect 5 Oran Berries. You could do these online (with 3 other players) or with NPCs.