One sad Pokemon story could be about a trainer abandoning their Pokemon. For example, a trainer might leave their old and weak Pokemon in the wild because it couldn't keep up in battles anymore. The Pokemon would be left alone, confused and sad, having known only the company of the trainer before.
Well, James' sad story is tied to his family. His family had high expectations for him which he couldn't meet. They were more interested in their own status and wealth. James wanted a different life, one full of adventure and freedom. In Team Rocket, he hoped to find a place where he could be himself, but things didn't go as planned. He and his partners often mess up their missions, and he has to endure Jessie's temper as well. All these make his story quite sad.
There's the story of a Magikarp that was constantly made fun of for being 'useless'. It tried so hard to be strong but was always overlooked. However, it didn't give up and eventually evolved into a powerful Gyarados, but all those years of being mocked were really sad. Magikarp was often bullied by other Pokemon in the pond, and trainers would release it quickly thinking it was worthless. But it had a hidden potential that took a long time to be recognized.
Well, it could be about a Pokemon that gets separated from its trainer. Maybe the trainer had to release it for some reason, like not being able to afford to keep it. The Pokemon then has to fend for itself in the wild, which is really sad.
Well, Cubone's sad tale begins with the loss of its mother. Cubone is often seen as a very lonely Pokemon. It wears the skull of its mother, which is a constant reminder of her absence. The skull also serves as a form of protection for Cubone. It wanders around, perhaps longing for the presence of its mother, and this sense of loss is what makes its story so sad.
Mewtwo was created in a lab through cruel genetic experiments. It was made as a clone of Mew but was constantly treated as a tool. It was isolated and experimented on, which made it feel a great deal of pain and loneliness. It had to struggle to understand its own existence and purpose in a world that seemed to only want to use it for power.
There was a Pikachu. Its trainer was really into winning battles. One day, Pikachu got seriously injured in a battle but the trainer still forced it to keep fighting. Eventually, Pikachu lost its ability to use its most powerful electric attacks. The trainer then decided to replace Pikachu with a stronger Pokemon. Pikachu was left at a Pokemon center, feeling abandoned and sad as it watched its old trainer leave with a new Pokemon.
One possible main character could be a Pikachu that lost its trainer in a storm. The Pikachu then has to search for the trainer all alone, facing all kinds of dangers in the process.
Well, a 'pokemon sad raichu fanfic' could be about a sad Raichu. Maybe it's about Raichu being separated from its trainer, feeling lonely and left out. It could also be that Raichu has lost in battles too many times and has become sad and lost its confidence.
Loss is a common theme. It could be the loss of a Pokemon, like in a battle or due to illness. Another theme is separation, such as when a trainer and Pokemon are forced apart.