I'm not sure specifically as there could be many different 'the flash barry gay fanfic' stories. Generally, it might be a fan - created fictional work that focuses on Barry from 'The Flash' in a gay - themed storyline. It could explore relationships, adventures or character development within that context.
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.
Yes, there are likely fanfictions out there with such a plot. 'The Flash' has a large and creative fanfiction community, and the idea of Barry and Caitlin having a pregnancy could be an interesting exploration of their relationship in the fan - created stories.
One of the best is 'The Flash: Rebirth'. It delved deep into Barry Allen's return and his complex relationship with the Speed Force. It also reintroduced many elements of his character and his place in the DC Universe.
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.
Well, in 'the flash dark barry fanfiction', a frequent theme is the loss of control. As Barry turns dark, he often loses the control he once had over his powers and his actions. Also, the theme of isolation is common. His friends and family may start to distance themselves from him, which makes him even more isolated and prone to further darkening. There's also the theme of redemption, as some stories explore whether he can come back from his dark state.
Barry Allen became The Flash after being struck by lightning while working in his lab. The lightning was charged with chemicals, which altered his body's chemistry and gave him super - speed. This event transformed him into the Scarlet Speedster we know as The Flash.
There are many great authors in this area. One popular one might be someone who goes by the name 'FlashFan123'. Their works often have really in - depth characterizations of Barry and Caitlin.