One common theme is the clash of ideals. Stain has his extreme views on heroes, while Deku is the epitome of the traditional hero concept. Another theme is redemption. Sometimes Stain is shown on a path of redemption through his interactions with Deku.
In the fanfiction, perhaps Stain trains Izuku because he believes Izuku has the purity of heart to use power in a way that Stain deems correct. Stain could teach Izuku how to analyze opponents better, which would enhance Izuku's ability to strategize in battles. Izuku might then start to question the current hero ranking system during his training. He could grow to be a hero who is more focused on the essence of heroism rather than just fame and recognition, which would make him stand out among his peers and also cause some friction with the more traditional heroes and hero agencies.
Finding the best 'stain x deku fanfic' can be a bit of a search. However, 'Unlikely Allies' is a fanfic that stands out. It begins with Stain initially being hostile towards Deku but as the story progresses, they find common ground. The author does a great job of writing their interactions, from tense stand - offs to moments of mutual understanding, all while staying true to the characters' personalities from the original source material.
Izuku would likely become more cynical. Stain's views are quite extreme, and being trained by him would expose Izuku to those ideas. He might start to question the motives of other heroes more often.
In these fics, the theme of morality often comes up. Stain has a very black - and - white view of heroes and villains, and fics will often question or expand on that. Additionally, the theme of his influence on other characters, especially the younger ones, is quite prevalent. His actions and words can inspire or terrify those who come into contact with him, and this is a recurring idea in many 'bnha stain fanfic'.
One of the main themes is the idea of identity. The characters in the novel struggle with how they are perceived and how they truly are. For example, Coleman Silk has a complex identity that he tries to hide. Another theme is the power of secrets. The secrets the characters hold have a great impact on their lives and relationships. Racism is also a theme, as Coleman's attempt to pass as white has implications related to race in society.
One popular type might be a Stain crossover with other well - known anime characters. For example, a crossover with All Might could explore an interesting dynamic where their opposing views on heroism clash. Another could be a Stain crossover with Deku, perhaps showing how Deku's ideology might be challenged or changed by interacting with Stain.