A common theme is the underdog story. Deku, being quirkless, is the ultimate underdog. He has to fight against the odds and the prejudice of a world that values quirks highly. This makes for a very compelling story as he overcomes these obstacles, often with Bakugo by his side or as his motivation.
One popular fanfiction concept could be Deku proving his worth without a quirk in the Bakudeku relationship. Maybe he uses his intelligence and strategic thinking to assist Bakugo in battles. For example, he could analyze opponents' weaknesses and come up with battle plans that Bakugo can execute. This would show that even without a quirk, Deku is an important part of their duo.
One common theme is the exploration of the alpha - omega relationship between Bakugo and Midoriya. It often involves power dynamics, with Bakugo's alpha nature sometimes clashing with Midoriya's omega traits.
Perhaps Deku discovers a dark secret about the origin of quirks and decides that the world would be better off without them. So, he starts a villainous campaign to eradicate quirks. He could form an alliance with other outcasts who have been mistreated due to their lack of quirks or abnormal quirks.
Love and friendship are also big themes. Through time travel, Bakugo and Deku might realize how much they actually care about each other. In some fanfictions, their friendship deepens as they face challenges together in the past. It could also lead to a romantic relationship in some stories, as they see each other in a new light and understand each other better.
Often, the theme of acceptance is strong. Izuku has to deal with a world that sometimes doesn't accept quirkless individuals as heroes. Jirou can play a role in making him feel accepted and valued. And vice versa, Izuku can accept Jirou for who she is, quirks and all. This mutual acceptance can lead to a deep emotional connection between them, which is often explored in fanfictions.
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.
One great quirkless Deku fanfiction is 'The Quirkless Hero'. In this story, Deku uses his intelligence and intense training to outwit villains. He forms an alliance with other underdog characters. It's really inspiring to see how he overcomes the odds without a quirk.
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 common theme is empowerment. Female Deku is often shown as a strong and capable hero, breaking gender barriers in the My Hero Academia universe.
Often, there is the theme of inspiration. Deku is very inspiring in the original story, and in fanfiction, he can inspire Shoto to be a better hero. Also, self - discovery. They both are on a journey to discover more about themselves, their powers, and their place in the hero world. In fanfiction, this journey can be elaborated on in different and interesting ways.