No. In fanfiction, there are numerous male heroes. Fanfiction is a vast and diverse genre that features a wide range of characters. While Izuku Midoriya is a very popular male hero, especially in the My Hero Academia fandom, there are other male heroes from different series or even original male heroes created by fanfiction writers. For example, there could be crossovers where male heroes from other superhero universes are introduced into the story. Also, some fanfiction might focus on developing minor male characters from the original source into full - fledged heroes.
Such a fanfic can also explore the darker aspects of the 'My Hero Academia' world that may not be fully explored in the original. It can show how the society in that world might handle or overlook abuse cases, which can make fans think about the overall social structure in the series. Maybe in the fanfic, Izuku's abuse is related to his lack of a strong quirk at first, which reflects on the quirk - centered society in 'My Hero Academia'.
One great 'Boku no Hero Academia Izuku' fanfic could be one where Izuku discovers a new, hidden quirk within himself that's not related to One For All. This could lead to him having to train in a completely different way and form new relationships with his classmates as they all try to figure out this new aspect of his powers.
One aspect of Bakugou x Midoriya fanfiction could be the exploration of their complex relationship. They start as rivals in the series. In fanfiction, this can be developed into a deep friendship or something more. Writers might focus on how Bakugou's aggressive nature and Midoriya's more timid yet determined self interact. For example, a fanfic could show Bakugou slowly coming to respect Midoriya in ways he never expected, leading to a bond that's different from their traditional rivalry.
There's also 'Izuku's Harem Adventure'. In this fanfiction, the author creates unique scenarios where Izuku finds himself in the middle of a harem. It has great character development for not only Izuku but also the members of his harem, exploring their individual personalities and how they interact with Izuku.
His closest friends like Ochaco Uraraka and Tenya Iida would most likely side with him. They have always been there for Midoriya and share his values of justice and doing what's right. Also, those heroes who have seen Midoriya's growth and believe in his pure intentions would probably join his side.
Someone might think this because if they are new to fanfiction or only really follow a particular subset of fanfiction related to Izuku Midoriya. For instance, if they mainly read stories from a specific website or group of writers who focus a great deal on Izuku Midoriya, they may not be exposed to the wider range of male heroes in fanfiction. Also, if a person is really attached to Izuku Midoriya's character arc and story, they might subconsciously assume he is the only male hero in fanfiction without realizing the vastness of the fanfiction world.
In many fanfictions, Izuku and the Hero Killer have a complex relationship. Sometimes, Izuku might be portrayed as trying to understand the Hero Killer's motives, which are often misconstrued but rooted in a desire for 'true' heroism. This can lead to some really interesting character development for Izuku as he grapples with his own ideas of heroism in the face of such a radical view.
Bakugo is often paired with Izuku. Their complex relationship can add a lot of drama to the detective story. Bakugo might be reluctantly helping Izuku or even be a suspect in the case Izuku is investigating.