The main antagonist could be a power - hungry elder in Temari's own village. This elder might see Temari as a threat to their authority, especially if she has been getting too much influence or support from other ninja. So, they frame her for a crime that leads to her banishment.
It could be that Temari accidentally causes a major disaster during a joint mission with Konoha. The Konoha elders, fearing public outcry, banish her. Naruto, who has befriended Temari, doesn't believe she did it on purpose. He then sets out to uncover the real cause of the disaster, which may involve a hidden enemy who framed Temari. Along the way, he has to convince his village that banishing Temari was a wrong decision.
In 'Naruto x Temari banished' fanfiction, the theme of exile itself is explored in depth. How do they cope with being outcasts? Do they resent their villages or try to find a way back? Also, the theme of cultural exchange can be present. If they travel to different regions, they might encounter new cultures and ways of life, which in turn affects their own beliefs and values. This can be really interesting as it shows how their characters can be molded by new experiences outside of their familiar shinobi world.
They might become more reliant on each other. Since they are both banished, they are in a similar situation. They could form a stronger bond as they face the challenges of being outcasts together. For example, they would need to find shelter and food, and this shared struggle could bring them closer.
It could start with mutual respect. Naruto, despite being banished, still has his strong will and Temari would respect that. They might begin by sharing stories of their past and their respective villages. This would lead to a growing understanding of each other.
One popular 'Naruto x Temari banished' fanfiction might involve them being banished from their respective villages due to some political intrigue. In some fanfics, they end up starting a new life together away from the shinobi world's politics. They could use their skills to build a new community or something similar.
Perhaps Naruto, in his banished state, has some new and unique abilities that Temari is intrigued by. She decides to help him master these powers in secret. As they train together, feelings start to develop. Their relationship could then be a source of conflict between Konoha and Suna as the two villages have different views on Naruto's banishment and his newfound connection with Temari.
It could also be due to false accusations. Perhaps an enemy ninja managed to frame them for a heinous crime. Like they were made to look as if they had conspired to assassinate an important figure from another village. This would lead to their banishment as their own villages would want to avoid a full - scale war because of their actions.
In the fanfiction, Naruto might comfort Temari by simply being there for her. He could offer her a friendly shoulder to lean on and listen to her problems without judgment.
If Temari is feeling stressed about her role as a shinobi in diplomatic matters, Naruto could offer his own perspective. He might say 'I'm not always good at the political stuff either, but I've learned that being true to yourself and your village is the most important thing. You're doing great, and everyone can see your strength and determination.' This would boost Temari's confidence and comfort her in her role.