Love triangles can also be a common theme. There's often a sense of romantic tension between the three characters. Additionally, themes of loyalty and betrayal are present. The OC may have to choose between Madara and Hashirama at some point, or deal with their own sense of loyalty to both. It's a complex web of emotions and relationships in these fanfictions.
One common theme is friendship. Despite their differences, Madara, Hashirama, and the OC often form a unique friendship that transcends the normal boundaries in the Naruto universe. Another theme is power. The OC usually has some sort of power that either attracts or challenges Madara and Hashirama.
One common theme is the struggle against clan differences. Since their clans are often in conflict in the original Naruto lore, in fanfiction this becomes a major obstacle for their relationship. For example, they might have to keep their love a secret to avoid causing more strife between the clans.
Often, the theme of redemption is present. Fem Madara may be depicted as having a change of heart or being redeemed through her relationship with Hashirama. Additionally, the theme of sacrifice is common. They might sacrifice their own beliefs or desires for the sake of their relationship or for the greater good. The theme of loyalty also pops up a lot, as they are loyal to each other in different ways, which is interesting to explore in these fanfictions.
The theme of unrequited love is also quite popular. It's often depicted that one of them has feelings that the other is initially unaware of. And there's the theme of power balance. How their powers affect their relationship, whether it brings them closer or drives them apart.
Power is a common theme. Madara is extremely powerful, so often the oc either has to match his power level in some way or is in awe of it. For example, in some fictions, the oc might be a powerful ninja herself and they engage in epic battles together.
One common theme is power imbalance. Since Madara is a very powerful character, often the OC has to deal with his strength and influence, which creates interesting dynamics in their relationship.
One common theme is the complex relationship between them. Given their history in the Naruto series, fanfics often explore how their past rivalries and loyalties translate into a romantic context in a yaoi relationship.
One common theme could be the exploration of a very different kind of relationship between Hashirama and Madara. It might focus on how they handle this unexpected situation of mpreg. Another theme could be the impact on the Naruto world's politics or power dynamics, as these two are very important figures in the Naruto universe.
One common theme is the idea of forbidden love. Since Madara and Hashirama are from rival clans, their relationship goes against the norms of their society. Another theme is the power of love to change destinies. Their love could potentially change the fate of the ninja world. For example, it could prevent future wars between the clans.
Reconciliation is also a theme. Given the historical enmity between their clans, a lot of fanfics focus on how fem Madara and Hashirama work towards reconciling their clans through their relationship. They become a symbol of hope for a united future, and this theme adds a lot of depth to the stories.
One common theme could be the exploration of a very different kind of relationship dynamic between Madara and Hashirama. Since the mpreg aspect is added, it might focus on how they deal with the unexpected situation, like Hashirama's pregnancy journey and Madara's role in it.