Well, Izuku Midoriya is no doubt one of the most popular characters in these crossovers. His journey to become a great hero in My Hero Academia can be enhanced in fanfiction when elements from JoJo are added. He could inherit a stand that helps him better understand and control his One For All quirk. Another popular character is Giorno Giovanna. His ability to create life and his complex backstory can be blended with the hero - villain dynamics of My Hero Academia. And Momo Yaoyorozu, with her intelligent and creative quirk, can be paired with a JoJo character to create a unique team - up or rivalry in fanfiction.
Well, in some My Hero Academia JoJo fanfiction, there are crossovers where the characters' personalities are blended. Deku might take on some of Jonathan Joestar's noble traits. And in terms of the storylines, there could be a scenario where the One For All quirk is somehow related to a stand's power source. This could lead to a whole new adventure where Deku has to not only master his quirk but also understand the stand - like aspect of it.
They might be really surprised. Some characters could be flattered by the positive portrayals in the fanfiction, while others might be a bit annoyed if their personalities are misrepresented. For example, Deku might be shy but also happy to see new interpretations of his growth journey.
Shigaraki would likely be disgusted if the fanfic made him seem weak or less of a threat. He'd probably scratch at his neck in irritation. Dabi would be dismissive. He'd think fanfics are just a waste of time and not worthy of his attention. Toga, though, might be intrigued. If the fanfic had a lot of blood and gore in it, or if it focused on her relationships in an interesting way, she could be really into it.
A plot twist could be that the Quirk system and Stands are somehow related. Maybe there was an ancient event that split the power into two forms. This would open up a whole new exploration of the lore in both universes. Characters would have to reevaluate their understanding of their own powers and how they interact with those from the other universe.
Uraraka's zero - gravity Quirk could work well with a Stand like The World. She could make objects weightless and then use The World's time - stop to position them in the perfect place for a powerful attack. For example, making a large boulder weightless, stopping time, and then moving it right above an enemy before time starts again.
There's also 'Stand Users at U.A. High'. This fanfic has really cool crossovers of abilities. For example, it shows how Josuke's Crazy Diamond could be used in hero training scenarios at U.A. It also delves into how the students from My Hero Academia would react to the more out - there personalities from JoJo's, like Jotaro's stoicism.
One interesting plot point is the clash of power systems. In these fanfics, seeing how stands from JoJo's interact with quirks in My Hero Academia can be really exciting. For instance, how would a stand user deal with a villain whose quirk nullifies physical attacks? Another is the cultural differences between the two universes. The more flamboyant and often morally ambiguous nature of JoJo's characters compared to the more straightforward hero - and - villain setup in My Hero Academia creates a lot of tension and interesting character dynamics.
They may be either amused or annoyed. It depends on how they are portrayed in the fanfiction. If it's a positive and creative portrayal, they might be amused. But if it's a negative or inaccurate one, they could be annoyed.
Some characters might be intrigued. For example, Izuku Midoriya would probably be very interested in understanding how the Gamer Sparda powers work. He would see it as a new type of quirk to study and might try to find ways to incorporate the strategies used in the 'game' aspect into his own hero training.