Well, identity is a common theme too. In 'female Muzan fanfic', the exploration of what it means to be Muzan as a female in a world that is mostly dominated by male demons. There's also the theme of survival. How does a female Muzan survive in a world full of threats? Some fanfics might show her using her wits and power to outsmart her enemies and stay on top.
One common theme is the exploration of femininity in a typically male - dominated character. Since Muzan is male in the original, making her female in fanfiction allows for a different take on power and how a female demon might rule.
One great 'female Muzan fanfic' could be 'The Female Muzan's Ascent'. It explores a unique take on the character, showing her in different scenarios and with different relationships. Another one might be 'Female Muzan: A New Perspective' which delves into her backstory in an interesting way.
Transformation is another popular theme. It could be the reader - insert changing muzan, or the other way around. Maybe the reader - insert is transformed into a being like muzan, or muzan starts to change his ways due to the influence of the reader - insert. These themes add depth and intrigue to the muzan x reader fanfiction.
Yes, there are quite a few. Some focus on an alternate universe where they have to team up for some strange reason. For example, in one fanfic, they have to face a new common enemy that is even more powerful than Muzan. Tanjiro has to put aside his hatred for a while to deal with this new threat.
One common theme is friendship. A female Latios might form deep friendships with other Pokémon or humans. Another theme could be adventure, like going on a quest to save her home or find a lost treasure.
One common theme is gender equality. Since it's about female musketeers, it often shows them fighting against the gender norms of their time. Another is friendship. Just like in the original musketeer stories, the female musketeers form strong bonds with their comrades. Adventure is also a big theme as they go on various quests and missions.
Love and relationships are also common. Since she has a complex situation, her relationships with other characters, whether it's romantic or platonic, are often explored. For example, how she deals with her feelings for Akane while in her female form.
Friendship and rivalry are also common themes. Just like in the original story, a female Izuku would have friends and rivals. Fanfics might explore how these relationships are different or similar. For example, her relationship with Bakugo could have a new dynamic. It might also show how she bonds with female characters in ways that a male Izuku might not.
In 'female transformation fanfic', a prevalent theme is the struggle with identity. The transformation makes the female character question who she is now. Another common theme is the exploration of new possibilities. Since she has changed, there are new paths and opportunities for her. Additionally, the theme of growth is often present, as she develops as a person during and after the transformation.
One common theme could be leadership. Since a commissar is often associated with leadership roles, in fanfic, it might explore how the female commissar leads her troops or makes important decisions.