The reactions of pro heroes to Deku fanfiction could vary greatly. Pro heroes who are more outgoing and friendly, like Mirio, might actively seek out Deku fanfiction just for fun. He could be the type to laugh out loud at the creative and sometimes wacky ideas in the fanfiction. However, more serious pro heroes, such as Aizawa, might initially be skeptical about the whole concept of fanfiction. But if the fanfiction has some deep insights into Deku's character and his journey, Aizawa might start to respect it more.
One possible plot could be that Villain Deku is on a mission to undermine the hero society and crosses paths with Hero Deku. They engage in a fierce battle where Villain Deku taunts Hero Deku about his ideals. In the end, Hero Deku manages to get through to a small part of Villain Deku's conscience, leaving him with some doubts about his villainous path.
Villain Deku might start to question his villainous ways. Meeting Hero Deku could make him see the good in heroism. Hero Deku, on the other hand, could become more empathetic towards those who turn to villainy. He might realize that there are reasons behind it and not all villains are just 'evil' for the sake of it.
Some might feel honored. They see it as a form of recognition of their importance in Deku's story or in the overall My Hero Academia universe. For instance, Iida could see his friendship with Deku being explored in a fanfiction as a compliment to their real - life bond.
In fanfiction, a quirkless Deku often has to rely more on his wits. Canon Deku got One For All, but in fanfic, he has to find other ways to be strong. For example, he might study different fighting styles more intensively.
Toga could be an ally. Since she has her own complex relationship with the idea of heroes and villains, she might find Deku's transformation interesting. She could provide some of her unique skills, like shape - shifting, to help Deku in his villainous plans. Additionally, Twice might also join them because of his loyalty to Toga and his own sense of being an outcast in the hero world.
A possible plot is that Villain Deku has a plan to destroy a major hero institution, and Hero Deku has to stop him. But when they meet, Hero Deku realizes that Villain Deku was once like him, full of hope. This makes Hero Deku hesitant to fight at full force. Or perhaps Villain Deku has kidnapped someone close to Hero Deku, and during the rescue mission, Hero Deku tries to convince Villain Deku to change his ways. Also, they could be from alternate universes where the roles are reversed, and they are forced to interact and learn from each other.
For Hero Deku, his development could be shown by how he reacts to seeing his dark self. He might start to question his own beliefs and actions. For Villain Deku, his development could be in the form of a possible redemption arc. Maybe he starts to see the error of his ways through his interactions with Hero Deku. For example, if Hero Deku shows him kindness or understanding that he never received before.
Well, first of all, the element of novelty. Izuku being the youngest pro hero is not a common concept in the original story, so in the fanfiction, it brings a fresh perspective. His inexperience also leads to some comical and heart - warming moments as he learns on the job. Additionally, his interactions with the hero community at large, from the big - name heroes to the side - characters, are key elements that shape the story and his journey as the youngest pro hero.
In a Deku villain fanfic, perhaps Deku could form an alliance with some of the existing villains in the Boku no Hero Academia world. He might see potential in them that the heroes overlook. He could team up with Shigaraki, believing that together they could reshape the world into a more 'fair' place, according to his now - twisted view.