I haven't come across one, but you could try looking on specialized comic websites or social media groups focused on comics. Maybe someone there knows if such a comic exists.
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.
A 'villain deku x villain todoroki fanfiction' might focus on their backstories that led them to become villains. It could be that they were both wronged by the hero system in some way. Deku might have been rejected too many times or faced unfair treatment, and Todoroki could have some family - related issues that pushed him to the dark side. The story could then show how they form an alliance and start their villainous journey together.
In 'villain deku fanfiction', a frequent theme is the subversion of expectations. Since Deku was initially seen as a pure - hearted hero, seeing him as a villain completely turns that on its head. Another theme is the power struggle. He has to fight against the heroes he once called allies. The theme of identity crisis is also there. He is no longer the Deku everyone knew, and he has to redefine himself as a villain. There's also the theme of the dark side of heroism, showing that the very qualities that could have made him a great hero can be twisted into making him a terrifying villain.
One great 'villain Deku' story could be one where he turns against his friends due to a misunderstanding about hero society. He might start using his intelligence and powerful quirk in devious ways, like creating chaos during hero - villain battles to expose the flaws in the system.
Perhaps they get involved in a power struggle within the villain world. They want to prove themselves as the most feared villains. This could lead to battles with other villains and alliances with some unexpected characters. It could also involve them trying to steal some powerful artifacts or secrets from the hero side to gain an edge in their villainous activities.
One great 'Best villain Deku fanfic' is 'Villainous Deku: The Dark Ascent'. It shows Deku turning to the dark side in a very believable way. The author does an excellent job of portraying his inner turmoil and the reasons behind his transformation. Another one could be 'Deku's Villainous Reign' which has some really intense action scenes where villain Deku battles against his former friends. It's a thrilling read.
Definitely not. Deku's character arc in the manga is centered around his growth and development as a hero. There are challenges and difficulties, but he never turns to the dark side.