The theme of power and its corrupting influence is seen a lot. Azula's descent into madness because of her thirst for power is a major plot point in the series. Fanfics may explore this further, perhaps showing how Zuko and Azula deal with power in different ways, or how Zuko tries to prevent Azula from being completely consumed by it. Some fanfics also show how they both struggle with the legacy of their family's power - the Fire Nation's power - and how it affects their lives and choices.
One common theme is redemption. Zuko's journey of redemption is a big part of the show, and fanfics often expand on it, sometimes in relation to his sister Azula. For example, some fanfics explore how he tries to help Azula find her own path to redemption.
Some fanfics focus on what could have happened if Azula had made different choices. This often involves alternate timelines or universes. There are also fanfics that deal with Azula's childhood and how her upbringing by Ozai affected her. They might explore her relationship with her mother in more depth as well.
Since 'lemon' often refers to more adult - themed content, I cannot promote or discuss such themes. However, in general non - 'lemon' fanfics about Azula and Zuko might often have themes of family reconciliation, as they are siblings in the Avatar universe. There could also be themes of power struggle, redemption, and personal growth for both characters.
One common theme is family reconciliation. Given their troubled past as siblings, many fanfics explore how Zuko and Azula can overcome their differences and rebuild their relationship. Another theme is redemption, especially for Azula who has committed many wrongs in the original story.
One common theme is redemption. Zuko often goes back in time to right the wrongs he did in his original timeline, seeking to be a better person. Another theme is the power of knowledge. Since he has knowledge from the future, he uses it to change events, like preventing certain battles or saving lives. For example, in many fics, he might use his knowledge of Sozin's Comet to stop the Fire Nation's initial attack.
A theme that frequently appears is the power dynamic. Azula is a very powerful bender, and Zuko has his own journey of becoming strong. How this power dynamic affects their relationship is often explored in fanfictions. Also, the idea of forbidden love is there. Given their family situation and the events in the show, their love might be seen as something that goes against the norms, which adds an element of drama.
Well, the theme of family also often comes up. Zuko's family situation is complicated, and Mai is also affected by her family's expectations. Fanfics may explore how their relationship is influenced by their families. For example, how Zuko's relationship with his father affects his relationship with Mai. Also, the theme of growth is common. Both Zuko and Mai grow as characters in fanfics, learning more about themselves and each other.
Physical harm during battles is also a theme. Since Zuko is often in the middle of combat, fanfictions might depict him getting seriously injured. This could then lead to him having to deal with the physical pain as well as the worry of his friends and allies. Writers might explore how his relationships change or strengthen during his recovery.
Since the 'zucest' part is inappropriate, if we focus on just Azula and Zuko in general fanfics, common themes can be their struggle for power within the Fire Nation. For example, in some fanfics, they might compete for their father's approval which was a major aspect in the original Avatar story.
Another option is Reddit. There are subreddits dedicated to Avatar fanfiction. You can ask the community for their favorite Zuko and Azula fanfics, and they'll likely be more than happy to share some great reads. There are often discussions about different interpretations of the characters in fanfics as well.
One popular theme is their growth and redemption. For example, Zuko's journey from being an outcast to finding his place and how Sokka and Azula might be part of that process in different ways. Maybe Sokka helps Zuko understand certain aspects of the Water Tribe culture, and Azula has her own moments of self - reflection due to their interactions.