A possible plot could be that Barry Allen is running through time and space and accidentally disrupts the Glee reunion. He then feels responsible and decides to help make it the best reunion ever. He could use his super speed to bring in some of the old Glee members who couldn't make it initially. And in the process, the Glee characters teach him some valuable lessons about the power of music and friendship.
If Barry Allen joined the Glee reunion in fanfiction, he might bring a new perspective to the group. His experience of saving the world and facing challenges could inspire the Glee characters to be more confident and take risks in their performances. Also, he could use his superpowers to create some amazing visual effects during their shows, like running around the stage so fast that he creates a cool blur effect.
One idea could be that the Krypton OC has some unique powers due to their Kryptonian heritage that Barry Allen initially doesn't understand. For example, they might be able to manipulate a different form of energy that interacts strangely with the Speed Force. This could lead to a series of adventures where they have to figure out how to work together without their powers interfering with each other.
One idea could be that the original Glee club members reunite to put on a charity show. They face old rivalries resurfacing but also rediscover their love for performing together. Maybe some of them have become big stars and some are still struggling, and they learn from each other's experiences.
Maybe the OC is from a parallel universe where the rules of the Flash's powers are different. This could lead to a lot of exploration and conflict as Barry tries to understand and work with this new element in his world. The OC could bring new knowledge about speed force that Barry has never known before.
One idea could be that Barry Allen accidentally runs so fast that he breaches the multiverse and ends up in the Harry Potter world. He could use his super speed to help Harry and his friends in their battles, like quickly disarming Death Eaters. Another idea is that a spell from the wizarding world goes wrong and transports Harry Potter to Central City where he teams up with Barry to fight the Reverse - Flash. They could learn from each other's skills, Harry teaching Barry about magic and Barry teaching Harry about science and speed.
One common theme is his relationships, like his love for Iris. Many fanfictions explore how their relationship evolves or faces challenges.
Barry Allen x Savitar fanfiction often plays with the idea of alternate universes. Writers may create scenarios where they are not enemies but rather allies or even something more. This can lead to interesting character developments. For example, Savitar's time - related powers combined with Barry's speed could be used in unique ways to solve problems or face new threats that were not present in the canon storyline.
One idea is that Barry discovers a time - related threat that has the potential to erase Bruce Wayne's past, which in turn would change the present Gotham City. They have to race against time (literally for Barry) to stop this threat. Another could be that a meta - human is stealing high - tech equipment from Wayne Enterprises and using it for evil purposes. Barry and Bruce work together to track down this meta - human and retrieve the stolen tech.
Well, an interesting plot might be that Barry and Kara discover a connection between their powers at a deeper level. For example, their powers are linked to an ancient energy source. As they explore this, they grow closer. Or perhaps there's a plot where Kara is transported to Barry's universe and has to adapt to his world while they solve a mystery that threatens both their universes. There could also be a story where they are forced to hide their relationship from their respective superhero teams for some reason, adding a bit of drama to the mix.
One idea could be that Barry and Leonard are forced to team up against a new meta - human threat that neither can handle alone. They start off distrusting each other but as they face challenges together, they gradually develop a mutual respect. For example, the meta - human has the ability to manipulate time in a way that affects both of their powers. Barry's speed is thrown off and Leonard's cold gun malfunctions. So they have to figure out how to work around these issues and defeat the enemy.