Normally, a Pokémon's growth is guided by a loving trainer's expertise, but Pokémon are intelligent creatures with wills of their own -- meaning, sometimes they might opt for something a little different. Appearing early on in the anime, the Squirtle Squad is an example of what happens when Pokémon take matters into their own hands.
This troupe of sunglasses-wearing Squirtle banded together to cause mischief and, more importantly, to protect each other, setting them apart from everyone else Ash Ketchum met during his trek across the Kanto region and beyond, even to this day.
Early on Indigo League, while Ash was still building up his team, he and his friends wandered through a town with a Squirtle problem on its hands. Five local Squirtle, long since abandoned by their owners, had formed a punk gang and were causing mischief everywhere they went. One Squirtle stood out from the rest, wearing pointed sunglasses as opposed to the others' round ones, clearly the director of the mayhem. These Pokémon had determined that no human would ever love or protect them, so they banded together like stray dogs, relying only on each other. The Squirtles clashed with Ash's team, but that would only last until Team Rocket burst onto the scene.
Team Rocket, still fixated on stealing Ash's Pikachu, tricked the Squirtles into helping them. Pikachu needed a Super Potion to recover from their attack, and the Squirtle Squad even took Misty hostage to make sure there was no funny business while Ash retrieved the Super Potion with their help. In the end, though, the five Squirtle realized that Team Rocket were the real bad guys, and defeated the villains with Water Gun, sending them blasting off yet again. Peace had returned to the town, but the Squirtle Squad still had a score to settle with Ash.
The boss Squirtle was impressed with Ash's genuine care for all Pokémon, and decided that Ash was a trainer worthy of respect. So, the boss Squirtle abandoned its glasses and formally became Ash's sixth Pokémon, while the other four Squirtle became firefighters for this town and others in need. The Squirtles had gone from delinquents to heroes, inspired by Ash's team, and true to their word, the four Squirtle saved the day again and again from accidental fires and other disasters. Once in a while, Ash's own Squirtle reunited with its old friends in the line of duty, and did its fair share of fighting in between missions.
Despite not evolving into a Wartortle or Blastoise, Ash's Squirtle proved itself a gritty and resourceful Pokémon by challenging a wide variety of rivals and prevailing time and again. Squirtle won nearly twice as many matches as it lost, but the whole time, Squirtle never forgot its delinquent tough-guy roots, by staying in its Squirtle evolution stage and fighting alone with incredible tenacity worthy of any good-hearted punk.
After a long journey together with Ash, this Squirtle finally said good-bye, and rejoined the other four as a firefighting team. Both Ash and Squirtle did a lot of growing up together.