Prologue:
The Ooze
"Why are we always stuck with disposal duty?" James groaned. He hefted a barrel and opened the valve. Pounds of green sludge poured off the side of the lookout.
"Don't ask me, just dump!" Jesse snapped at him, doing the same.
Just then, Meowth joined them, dragging behind him another cart full of barrels. "AGGGGHHHH!" he groaned, audibly. When that got no response; "Thanks a lot for offering to help, guys."
James threw away his barrel in disgust. "You've got the better job, you know, so stop complaining. We actually have to smell this stuff."
It wasn't fair. When the three of them had joined Team Rocket, they thought it would be a life of adventure and danger. Yet here they were, dumping Giovanni's trash into a ravine. Yes, they were rookies, but didn't they deserve the benefit of the doubt?
"What is this stuff anyway?" Meowth asked, poking his head over the ravine.
Jesse gave him a swift boot in the back of the head. "I don't know, I don't want to know, and we aren't supposed to know. Now go get the last barrels!"
None of them actually knew what it was they were dumping. Their commanding officer had called them into Warehouse 3, and told them to take the barrels and dump them into the ravine near Headquarters. When James had asked what it was, they got yelled at for five minutes about "sticking their noses where they don't belong" and were then dismissed.
After a hour or two, the last barrel had been dumped into the ravine, and the three comrades laid on the ground, exhausted.
"Now what?" Jesse wheezed.
"We go back, sleep, and wake up to probably take out more garbage" Meowth said. The three picked themselves up off the ground, dusted off their uniforms, and slowly limped back to their barrack.
If they had stayed, they might have stuck their heads over the cliff edge to see the sludge they poured had formed a small pool. If they had stayed, they would have seen the Rattata that came down from the mountains searching for food, and accidentally slipped and fell into the ooze pool. If they had stayed, they would have seen the Rattata crawl out and limp away, and later, the group of four Squirtles that came to play in the ooze pool, thinking it was a small pond.
This was all fifteen years ago.