A common theme is the clash of powers. When Tomura crosses over with other universes, his own powerful abilities often come into conflict with the powers of the characters in those universes. For example, in a crossover with the X - Men, his decay power is pitted against the mutant abilities of the X - Men.
One popular Tomura crossover fanfiction is the one where he crosses over with the Avengers universe. It creates really interesting scenarios as Tomura's power and motives clash with the superheroes of the Avengers. Another great one is his crossover with the Harry Potter world, seeing how his dark nature would interact with the magic there.
In a crossover with the DC universe, the Joker could be an interesting character to pair with Tomura Shigaraki. Both are chaotic and have a disregard for life. Their meeting could lead to either a partnership in chaos or a battle for dominance in the criminal underworld.
One idea could be a crossover with the X - Men universe. Tomura Shigaraki's decay power could create interesting interactions with the mutants. For example, how would his power affect Wolverine's healing factor? Another could be a crossover with the Harry Potter world. Maybe he tries to infiltrate Hogwarts to steal magical artifacts, leading to battles with the students and teachers.
Dabi could be a great character to pair with Tomura. They are both villains and their powers and personalities could create some interesting interactions. Maybe they could team up for a particularly difficult mission or have a power struggle within the League of Villains.
One aspect of Mha Tomura x Himiko fanfiction could be the exploration of their unique relationship dynamics. Tomura's complex character, with his goals and his own brand of villainy, and Himiko's rather eccentric and blood - loving nature can create some really interesting interactions. Writers might delve into how they understand each other on a deeper level, perhaps sharing a common view of the world that is different from the heroes' perspective.
One common theme is identity. Since Tomura is male in the original, making her female in fanfiction often leads to exploring how this new identity affects her relationships and her role in the villainous world. Another theme is power. Writers often play with how a female Tomura might use or abuse her power differently.
One common theme is the exploration of his past trauma. Most of these fanfictions dig into what made him become a villain in the first place. Another theme is the power of forgiveness. Characters often have to forgive Shigaraki for his past deeds for his redemption to be possible.
A common theme is the exploration of their dark sides. Both characters are villains in the MHA universe, so fanfictions often focus on how their villainous natures interact. For example, they might plot together to take down a hero or cause chaos in the city.