One great Flash and Supergirl fanfiction is 'The Team -Up of Legends'. It shows an alternate universe where they have to work together against a powerful new villain. The story does a great job of portraying their different powers and how they complement each other in battle.
Another good one is 'When Flash Meets Supergirl'. In this story, Flash accidentally travels to Supergirl's dimension. The writer does an excellent job of describing the differences between their two worlds and how they overcome the initial confusion to team up. It's full of action and some really cool crossovers of their powers.
There's also 'Flash and Supergirl: The Bond'. This fanfiction focuses on the relationship between the two heroes outside of fighting villains. It shows how they become friends and support each other on a personal level, which is really interesting as it gives more depth to their characters.
A great moment could be when they first meet and realize how different yet similar their worlds are. Supergirl might be in awe of The Flash's speed, and The Flash could be impressed by Supergirl's strength. It's a moment of mutual respect that often sets the tone for the rest of the story.
Well, Cisco Ramon from The Flash would be a great addition. He could use his tech skills to create some new gadgets or figure out ways to counter the villains' powers. Also, Martian Manhunter from Supergirl's side. His shape - shifting and telepathic abilities would add a whole new dimension to the story.
One great Damian Wayne x Supergirl fanfiction is 'The Unlikely Alliance'. It beautifully weaves their different personalities together. Damian's brooding nature contrasts with Supergirl's more optimistic and hopeful outlook. The story has them team up against a common enemy, and as they work together, a slow - burning relationship begins to form.
If Barry kidnapped Supergirl in fanfiction, it could be a really interesting plot twist. Maybe Barry has been affected by some sort of red kryptonite - like substance that makes him act out of character. This would lead to a conflict between the Flash and Supergirl's friends and allies. They would be confused as to why Barry would do such a thing.
There's a fanfic called 'Nightwing and Supergirl: United Front' which has great character interactions. It shows how they work together in battle and also their off - battle banter which is really engaging.
One of the best places to find Flash and Supergirl fanfiction is Archive of Our Own (AO3). It has a large collection of fan - created stories that cover all kinds of scenarios and relationships between the two characters. The site is well - organized, making it easy to search for specific tags or themes related to Flash and Supergirl.
One idea could be that a powerful villain threatens both their cities simultaneously. Supergirl and The Flash have to team up, and in the fanfiction, their different powers and personalities could lead to some interesting interactions. For example, Supergirl's strength and The Flash's speed could be combined in unique ways to defeat the villain.
A plot twist could be that a character from one of the shows, who seems to be a minor or unassuming figure, is actually a powerful being from the future sent to manipulate the events of the crossover. This person has been subtly guiding the actions of the heroes, and when the truth is revealed, it completely changes the heroes' perception of the events they've been through and who they can trust.
Another possibility is that Barry was kidnapped himself first and then forced to kidnap Supergirl. The real kidnappers could be a group of meta - humans who want to create chaos by pitting two of the most powerful heroes against each other. Barry would be in a difficult situation, having to do something against his will, and Supergirl would initially be confused and angry at Barry until they both figure out what's really going on.
Definitely, Cisco Ramon from Flash. He can add some tech - savvy humor and his ability to create new gadgets can be really useful in the crossover. For example, he could make a device that helps Supergirl deal with a new type of kryptonite - like threat.