One idea could be a story where Red and Blue have to team up to face a new, extremely powerful and mysterious Pokemon that threatens the entire region. They start off with their usual rivalry but gradually learn to trust and rely on each other more as the adventure progresses.
A plot could revolve around Red and Blue getting transported to a parallel universe where their roles are reversed. Blue is the quiet and reserved one, while Red is the more brash and outspoken. They have to figure out how to get back to their own universe while also dealing with the differences in this new world and their changed personalities in relation to each other.
Professor Oak can be included. He could be the one who gives Red and Blue important missions or tasks. His wisdom and knowledge of Pokemon can guide the two protagonists in their journey. For example, he might provide them with crucial information about a rare Pokemon they need to find to achieve their goals in the fanfiction.
One idea could be exploring an alternate timeline where Red and Blue have different starter Pokemon. Maybe Red starts with Squirtle instead of Charmander, which would change the dynamics of his battles and relationships with other trainers.
One plot idea could be a girl trainer in the Pokemon Red and Blue world who discovers a rare and powerful Pokemon that no one has ever seen before. She has to protect it from evil teams who want to use it for their own gain.
One plot idea could be the characters from Red vs Blue and RWBY teaming up to fight a common enemy. For example, a powerful Grimm that has somehow entered the Red vs Blue universe. Another could be the Reds and Blues getting involved in the Beacon Academy's classes and causing chaos with their unique combat styles. Maybe they could introduce their own brand of humor to the more serious RWBY world.
One idea could be a story where the main character is a Pokemon trainer who discovers a rare and powerful Pokemon that no one has ever seen before. They then have to protect it from evil organizations who want to use it for their own gain.
One idea could be a team - up. The Reds and Blues get transported into the Overwatch universe and have to team up with the Overwatch heroes to fight a common enemy like a new, powerful omnic threat. Another could be a competition where the Reds and Blues think they can outdo the Overwatch heroes in a mission, leading to some humorous misunderstandings.
One idea could be a story where a unique Pokemon only found in the Red version teams up with a trainer from the Blue version to face a new, powerful threat. Another could be a story about a trainer who discovers a secret connection between the Red and Blue Pokedex that leads to an adventure.
Maybe the Caboose could cross over into a world where the rules of combat are completely different. His Red vs Blue training would be put to the test, and he'd have to adapt quickly. For example, instead of using guns, they use magic or some other form of power. The Caboose might initially be confused but then find his own way to contribute.
Maybe a story where the Reds and Blues are transported to the RWBY world. They have to learn about Grimm and Huntsmen while trying to find a way back home. Along the way, they could team up with RWBY characters like Yang, who could teach them some hand - to - hand combat skills, which are different from their usual long - range tactics.
One idea could be that the Reds and Blues get transported to the RWBY world and have to learn how to use Dust to fight. They could team up with Team RWBY and face off against a new enemy that is a threat to both their universes. Maybe they introduce their unique sense of humor and combat styles to the RWBY characters.