Gale might also attempt to rescue Katniss. He's her friend from District 12 and is quite skilled in his own right. He would be furious to hear that Cato has kidnapped Katniss and would likely gather resources and allies to try and save her.
One possible plotline could be that Cato kidnaps Katniss as a strategic move in the Hunger Games. Maybe he thinks he can use her to draw out other tributes or get an advantage over the Careers. Another could be that Cato has some sort of personal vendetta against Katniss that leads him to kidnap her outside of the normal rules of the Games.
For Katniss, her focus would change. Instead of just fighting for the districts or her own survival, she'd be fighting for her unborn child. This could make her more strategic in a different way. Cato, on the other hand, would probably have to confront his past actions in the Hunger Games more deeply. He might feel the need to redeem himself in the eyes of Katniss and their future child, which could soften his hard - edged personality.
One common theme is the idea of enemies - to - allies. Given their opposing stances in the Hunger Games, many fanfictions explore how they could come to work together or understand each other. Another theme is unrequited love or a forbidden love, as their different districts and roles in the Games make a relationship between them seem impossible in the context of the story's world.
One possible fanfiction could be about Katniss and Cato being forced to team up in an alternate version of the Hunger Games. Maybe they realize that the Capitol's control is the real enemy and start to work together to undermine the system from within the arena.
A Cato and Katniss love story in fanfiction often plays with the idea of redemption. Cato, who is initially portrayed as a brutal competitor, might find redemption through his love for Katniss. Fanfiction writers could show how Katniss, with her strong will and kind heart, could break through Cato's tough exterior. Their love could develop as they realize they are both victims of the Capitol's cruel games. It could be a story of two broken souls finding solace in each other.
One possible plot could be that in an alternate universe where the Hunger Games have a different set of rules. Katniss and Cato are forced into an unexpected alliance due to some strange Capitol decree. As they spend time together, feelings develop in a very unexpected way and Katniss becomes pregnant. This would lead to a huge shift in their relationship dynamics and also their standing in their respective districts.
Well, it could be that in this fanfiction, they are forced into marriage by the Capitol for some sort of twisted entertainment. Katniss would be very resistant at first, but Cato might gradually show a different side of himself, and they could start to develop an unexpected bond.
One possible plot could be that after the Games, Cato somehow survives and he has a change of heart. He realizes the horror of the Games and starts to see Katniss in a new light. They bond over their shared trauma and eventually fall in love and get married.
Yes, there are some out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'Cato marries Katniss' in the search bar and you might find some interesting stories that explore this alternate scenario.