One common theme is growth. Both characters often grow as individuals and in their relationship. For example, they might learn to overcome their insecurities or past rivalries. Another theme is the power of friendship evolving into love. They start as classmates or rivals, and then their bond deepens into something more romantic.
For Villain Deku, start by showing his gradual descent into villainy. Maybe he starts having doubts about the hero system and those doubts fester. For his relationship with Kacchan, show how his feelings change from friendship (or rivalry) to something more complex. For Kacchan, show his initial shock and anger at Deku's turn. Then, have him start to question if there was something he could have done to prevent it. As the story progresses, he could start to see the good in Deku again.
Well, a plot could involve a power struggle. Villain Deku has some new and dangerous powers that he uses to challenge Kacchan. Kacchan, being the proud hero he is, refuses to back down. Along the way, they start to understand each other better. Maybe Deku's villainy is a result of some misunderstanding or being pushed too far by the hero society. As they interact more, they might find a way to reconcile their differences and even work together to change the hero society that led Deku astray in the first place.
One popular 'deku x female kacchan fanfiction' might be 'A New Bond'. In this story, Deku and female Kacchan start to see each other in a new light after a shared adventure. Their relationship develops as they face challenges together and learn to understand each other's strengths and weaknesses.
One common theme is friendship development. They might start off as just classmates but then grow to be really good friends. Another could be about them working together in a mission and learning to trust each other.
It's highly inappropriate. The original works that these characters come from are often aimed at a wide range of audiences, including younger viewers. Writing such sexual fanfiction not only violates the spirit of the original work but also may expose inappropriate content to an unintended audience. It's better to focus on creating positive, character - developing fanfiction that stays true to the essence of the source.
The main differences are in their expressions and some minor details of personality. In the manga, Deku might seem a bit more intense, while in the anime, he's sometimes presented a bit softer.
I'm not sure of specific 'kacchan x uraraka fanfic' titles off the top of my head. But you can also check out Tumblr. Sometimes fans share their favorite fanfics there, and you might be able to find some really interesting ones that explore the relationship between Kacchan and Uraraka in creative ways.
In 'deku meets future deku fanfiction', perhaps the future Deku warns the present one about upcoming threats. He could tell him about villains he'll face in the future and how to defeat them. This would give the present Deku an edge in his battles and also in his growth as a hero.