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.
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.
In a fanfiction scenario where Barry is stabbed during a Flash - Supergirl crossover, it could lead to a lot of interesting plot developments. Maybe Supergirl would have to step up and use her powers in new ways to protect Central City in Barry's absence. She might have to team up with the other members of Team Flash more closely.
Well, the plot could involve Supergirl and Barry initially meeting during a multiverse - related crisis. They might start as allies, but as they work together more often, Supergirl begins to notice Barry's kind heart and his determination. She could be drawn to his unique sense of humor as well. Their relationship might develop slowly, with them sharing their secrets and fears, and eventually realizing they have fallen in love. It could also involve some challenges like having to keep their relationship a secret from their respective teams at first.
Perhaps in this fanfiction, Barry's death causes a rift in the multiverse. Supergirl then has to team up with other heroes from different universes to try and fix it. His death could be the start of a much larger threat that only a united front of heroes can face. She might struggle with the guilt of not being able to save him at first but then turns that into motivation.
If Barry was stabbed, the story would change drastically. His speed is what often saves the day, so without it, the villains would have an upper hand. Supergirl would have to cover more ground and face tougher challenges alone or with less - experienced allies.
If Supergirl and Barry are in a relationship in the fanfic, their powers could interact in some interesting ways. For example, Barry's super - speed could be used to enhance Supergirl's combat abilities. He could quickly move her around the battlefield, allowing her to surprise enemies. Supergirl's strength could protect Barry when he's vulnerable during his high - speed runs. They might also combine their powers to create a sort of 'super - blast' by having Supergirl charge up an energy attack while Barry spins around her at super - speed to amplify it.
If Barry dies in a fanfiction crossover, it could lead to a power vacuum. This might cause other villains to become bolder. For example, the Rogues might try to take over Central City without the Flash to stop them. Supergirl would then have to step in and deal with a situation she's not entirely familiar with, which could change the dynamics of how she operates in the DC Universe.
In Star Labs, they could encounter other characters from their respective universes who are also there for some reason. They might team up with them to solve a mystery related to the lab's latest research. For instance, there could be a strange energy source that they need to figure out. Kara's super strength and Barry's quick thinking would be put to use. They could also have some friendly competitions within the lab, like who can complete a certain task faster or more accurately, which would add some light - heartedness to their time in Star Labs.
The scientists in Star Labs could be very curious about Kara. They would want to study her abilities, like her flight and super strength. But some might also be a bit cautious at first, not knowing exactly what she's capable of. However, as they get to know her better, they would start to trust her and maybe even ask for her help with certain projects.