A possible plot could involve the banished mercenary being from a long - lost clan. The reason for his banishment was a false accusation by a rival clan. As he wanders the Naruto world as a mercenary, he discovers clues about his clan's true heritage and power. He then uses his skills as a mercenary to gather allies and resources to prove his clan's innocence and restore its honor. Along the way, he crosses paths with Naruto and his friends and they either help or hinder his quest depending on the situation.
One idea could be that the banished mercenary has unique jutsu skills learned from different lands during his mercenary days. He could return to the Naruto world with a new perspective and hidden motives, perhaps trying to unite different ninja clans against a new, greater threat. Another plot idea is that he has a connection to an ancient prophecy that was thought to be forgotten, and his banishment was actually part of a grand scheme to protect him until the time was right.
One idea could be that Naruto and Tenten are banished due to a false accusation of plotting against the village. They then have to prove their innocence while on the run. They might encounter old enemies who have also been exiled and form an unlikely alliance to clear their names.
One idea could be that the character with the Sharingan is banished due to false accusations of using its power for evil. He then has to journey alone, facing challenges and learning to control his power in new ways. Maybe he meets a group of outcasts who he befriends and together they fight against the unjust system that banished him.
One plot idea could be Naruto being banished to the world of One Piece. He could join the Straw Hat Pirates and use his ninja skills in new and exciting ways. For example, his shadow clone jutsu could be used for various tasks on the ship. Another idea is that he gets banished to the Bleach universe. He might learn about Soul Reapers and Hollows, and his chakra could be seen as a unique form of spiritual energy there. Maybe he could even train with the Soul Society to become stronger.
For the banished mercenary, his character development can be made interesting by exploring his backstory. If he was banished because of a misunderstanding, gradually revealing the truth behind it can be a great way to develop his character. He might initially be a lone wolf, but as he gets involved in various adventures, he realizes the importance of having comrades. His views on the shinobi way could change over time. For instance, he might start off believing that only power matters but then, after seeing the selfless acts of others, he begins to understand the value of things like loyalty and friendship. This transformation from a jaded mercenary to someone with a more positive outlook on the shinobi world would be very engaging.
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.
One plot idea could be that Naruto, after being banished, crosses paths with Kurenai who is on a solo mission. She initially has her doubts about him due to his banishment but gradually realizes he was wrongly accused. They team up to face a common enemy that threatens the village from afar. This could lead to a growing bond between them.
One interesting plot could be that Naruto is betrayed by the Hidden Leaf Village due to false accusations of being a spy for a powerful enemy. Banished, he then discovers new powers or allies outside the village. He might form his own group of outcasts and come back to the village to prove his innocence and seek revenge on those who wronged him.
One idea could be that the banished Naruto discovers the female Kyuubi's true nature. He realizes she's not just a force of destruction but has her own emotions and desires. As they interact, Naruto starts to see her as an ally. For example, she could help him gain new powers in secret while he's exiled, and together they plan to prove his innocence to the village.
Perhaps there's a political conspiracy in the village. Naruto and Shikamaru discover some dark secrets that certain powerful people in the village don't want exposed. So, they are banished to keep them quiet. They then form an alliance with other outcasts and work towards uncovering the truth and returning to the village to set things right. This could involve a lot of action scenes as they fight off those sent to stop them.