A fascinating plotline could be that Indra and Asura are sent on a journey through different dimensions by some ancient jutsu. In these dimensions, they see different versions of themselves and their story. They learn from these experiences and come back to their world with a new perspective, which could potentially change the course of the Naruto universe.
One interesting idea could be the exploration of how the reincarnation affects Naruto's relationships. For example, how it changes his bond with Sasuke, as Sasuke is often linked to Indra. Maybe it could lead to a deeper understanding between them, beyond their normal rivalry.
Well, perhaps a plot where Asura and Indra are given a chance to rewrite their history. They start to understand each other's viewpoints better and try to create a new future for the ninja world. They could also meet their descendants, like Naruto and Sasuke, in a different dimension and exchange knowledge and power.
One idea could be exploring their relationship in a modern AU. Imagine Indra and Asura as two brothers in a modern city, dealing with normal life problems while still having their spiritual connection. They could struggle with family expectations, like Indra being the over - achieving older brother and Asura the more laid - back one, but they have to come together to face a common threat that has a connection to their past lives.
Often, other characters from the Naruto universe also make appearances. For example, the various ninja clans like the Uchiha and the Senju. Their loyalties and relationships with Indra and Asura can add depth to the story. Maybe there are also some original characters created by the fanfiction writer to interact with Indra and Asura and drive the plot forward in unique ways.
A fanfic could focus on a time - travel plot. For example, Asura or Indra gets sent to a different era and has to adapt while also finding a way back. Along the way, they encounter versions of themselves or each other from that time and have to deal with the consequences of interfering with the timeline.
Madara could also be a suitable antagonist. Imagine if he somehow came back to life and found out about Asura and Indra's reincarnation. He would surely try to use them for his own goals, or maybe try to prove that his way of thinking was right all along. He could also use his knowledge of the Sharingan and Rinnegan to create new challenges for Asura and Indra.
One common theme is the struggle against society. Since their relationship might be seen as unconventional, they often have to face opposition from the world around them.
One possible plotline could be Dark Naruto's struggle with the Asura power within him. He might have to face inner demons and temptations that come with this power. For example, he could be constantly on the verge of losing control and harming those he cares about.
The concept changes the relationships too. Naruto's relationship with Sasuke could be seen in a whole new light. Since Sasuke is related to Indra, they might have a more fated connection. They could be forced to work together more often to fulfill some greater destiny related to their reincarnation status. Also, the way other characters view Naruto could change. They might see him as a more significant figure in the grand scheme of things, not just as a powerful ninja but as a key part of a long - standing cycle.
One interesting Indra Naruto fanfiction could be 'Indra's Redemption'. In this story, Indra might be given a chance to change his path and work towards a better future for the ninja world. It could explore his complex relationship with Naruto and how their interactions shape both of their destinies.