One common theme is the passing on of the hero legacy. All Might would be in a unique position to train Izuku and teach him everything he knows about being a hero. Another theme is the exploration of family secrets. How did Izuku not know All Might was his father? And how does this revelation change their relationship and the world around them?
Another theme could be sacrifice. Inko might sacrifice her own comfort or safety for Izuku's well - being. Fanfics often play with this idea, showing how deep their love for each other is.
In 'female Izuku is a bunny' fanfics, a recurring theme could be the relationship between Izuku and other characters. For example, how her friends or potential love interests react to her new form. Some fanfics might also focus on her origin story as a bunny - like being, perhaps she was experimented on or it was a quirk - related transformation. Additionally, the fanfic could explore how she copes with the physical and emotional changes that come with being a bunny in a world full of heroes and villains.
In 'bill is dipper's dad' fanfics, the theme of discovery is quite common. Dipper discovers this strange new aspect of his family tree, and that sets off a chain of events. There's also the theme of conflict. Given Bill's nature, there would be internal and external conflicts. Internally, Dipper might struggle with accepting Bill as his father, and externally, they might face opposition from other characters who find this relationship unacceptable or dangerous. Additionally, the theme of destiny could play a role, as if this relationship was somehow fated and what that means for both of them.
Comfort is also a big theme. In these fanfics, they are each other's source of comfort. When Izuku has a bad day, maybe because he got scolded by a teacher or he failed at something, Tsuyu is there to cheer him up. And when Tsuyu is feeling down, Izuku's positive energy and determination rub off on her. This mutual comfort creates a really warm and fuzzy feeling in the fanfics.
One common theme is family. Since Sirius is now Harry's dad, the fanfics often focus on building a strong family unit. Another theme could be redemption, as Sirius might have more of a chance to make up for his past mistakes. Also, there's the theme of protection, as Sirius would be even more determined to keep Harry safe from Voldemort.
One common theme is friendship. Izuku is often depicted forming strong bonds with his classmates like Bakugo, Uraraka, and others. These friendships help him grow as a hero. For example, in many fanfics, they train together and support each other during difficult times.
One common theme is family support. Since Aizawa is a strong and experienced hero, he can offer Izuku a lot of support, whether it's in training or dealing with the challenges of being a hero - in - training. Another theme could be the discovery of their relationship. Maybe Izuku didn't know Aizawa was his brother at first, and the fanfic could focus on how they come to terms with this new family connection.
Friendship and rivalry are also common themes. Just like in the original story, a female Izuku would have friends and rivals. Fanfics might explore how these relationships are different or similar. For example, her relationship with Bakugo could have a new dynamic. It might also show how she bonds with female characters in ways that a male Izuku might not.
A major theme is the struggle against overwhelming expectations. Izuku has high expectations from himself and others in the world of the story. When he fails to meet them, it leads to his depression. Also, the theme of lost hope is common. He might lose faith in his dreams and his ability to become a hero. In some fanfictions, his depression is also linked to past traumas, like being bullied for not having a quirk initially.
One common theme is innovation. Izuku uses his scientific skills to come up with new things like advanced support gear or ways to improve quirks. Another theme is the underdog story. Even though he's a scientist, he may face challenges from traditional hero types who don't understand his methods.