Team Rocket's roots in Kasei began sixty-five years ago, when Giovanni was in his prime and touring the country's gyms. Watching battle after battle with these mysterious Fusions impressed the man, if these creatures could become this powerful on their own, what if he could control them? Train them to become elite warriors for the Rocket cause? The possibility intrigued him, to the point he returned with his board of executives on his next visit to the region. They all agreed unanimously: Fusions were a ripe berry to be plucked, but the time it took to strengthen the mythic bond between the Pokemon and Humans took far too long to build an army. There had to be a better way; A way to exploit it.
A secret headquarters was erected to the region just north of Kasei: Chugoku. Giovanni himself headed the research team, and Team Rocket's top scientists went to work around the clock studying Kasei's population in secret. Around this time, many Fusions went missing in North Kasei; kidnapped for the research. The project continued steadily for five years, until they finally hit a breakthrough. Rocket scientists built a machine that allowed them to forge an artificial bond between Pokemon and Human, allowing them to fuse immediately.
Quickly they amassed an army by forcing their most powerful Pokemon to fuse with their grunts, and turned their sights on taking Japan by force, starting with Kasei. They had taken all of northern Kasei when the tides started to turn. A hero infiltrated the Rocket Headquarters in Chugoku, and found the mastermind behind the invasion, Giovanni. The result of this battle is unknown to the common man, but Giovanni and the hero disappeared afterwards and haven't been seen since. Without their leader guide them, the adventuring Teams of Kasei united, and the most powerful trainers in the region poised a final battle against Team Rocket's army. They proved to be too much to the invaders, and Team Rocket was driven back into hiding. The aftermath of the war continues to be felt by Team Rocket, who is now headed by Executive Thorn. A small faction of the Team Rocket continues to believe their true leader will return one day, who are referred to as the Neo Genesis, or the "New Beginning" Rockets.