A possible idea for a MHA RWBY crossover fanfic is to explore the idea of semblance and Quirk evolution. The characters from both shows could train together and discover new ways to enhance their abilities. For instance, Izuku Midoriya could learn from Ruby about using her Crescent Rose in combat and in turn, show her how to better control her power flow. The cultural differences between the two worlds could also add depth to the story, like how the heroes in MHA are more publicly recognized compared to RWBY, and how the characters react to this disparity.
One interesting crossover could be the magic system of Harry Potter being introduced to the MHA world. For example, a character from MHA might discover they have magical abilities like a Hogwarts student. Another could be the heroes from MHA having to face off against dark wizards from the Harry Potter universe. It would be a really cool mix of the two different power dynamics.
A lot of MHA Kaminari x Jirou fanfictions focus on the idea of mutual understanding. They come from different backgrounds and have different quirks, but through getting to know each other better, they grow closer. There are also themes of jealousy, like when one of them might get a bit jealous if the other is spending too much time with someone else. Also, their shared experiences at UA, like going through tough battles together, are often used as a theme to bring them closer in the stories.
To some extent, it is popular. There are many online platforms where MHA adult fanfiction can be found. The popularity might stem from the fact that the MHA world has a rich cast of characters and a complex universe. Fans who enjoy adult - oriented storytelling might use these characters to create their own narratives that are more in line with their interests in terms of relationships, power dynamics, and personal growth, all with an adult twist.
Well, without having read it directly, it could potentially be about RWBY characters attacking this 'Ben' in a scenario that the author of the fanfiction has devised. Maybe there's some sort of power struggle or personal vendetta within the RWBY universe combined with the addition of this 'Ben' character. It could also be a misinterpretation of a more complex relationship that the fanfiction is exploring.
To create a believable plot, first establish a common threat. It could be a powerful villain or a strange phenomenon that affects both universes. Then, gradually introduce the characters from each world to each other. For example, start with a small group of MHA characters accidentally ending up in RWBY's world. Their reactions to the new environment and the differences in technology and power systems can drive the plot forward.
No, it's not appropriate. Deku is a character with his own depth, goals, and story within the MHA universe. Fanfic should aim to explore his hero journey, his relationships in terms of mutual respect and support, not create content that focuses on inappropriate or disrespectful ideas like this.
I think Harry Potter himself would be very powerful in this crossover. He has the experience of fighting dark wizards and his magic skills. If he was in the MHA world, he could use his magic to enhance his physical abilities like the characters with quirks. His ability to resist the Imperius Curse and his knowledge of defensive magic would give him an edge over many MHA villains.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are a ton of MHA fanfictions there, and you can specifically search for Kaminari x Jirou ones. Another option is Fanfiction.net, though the quality can be a bit more variable. You could also check out Tumblr, as some users post links to their favorite fanfictions or even write short ones themselves.
I think All Might's reaction would be interesting. He might see Loid as a kind of hero in a different sense. Loid's selfless dedication to his mission to prevent war, even if it means living a double life, could remind All Might of his own role as a symbol of peace. All Might would probably respect Loid's determination.