It could be that Naruto's brash and impulsive nature during missions causes too many problems for Team 7. For example, he rushes into battles without proper planning, which nearly gets his teammates killed. This leads to a decision within the team, led by Sasuke who feels Naruto is holding them back, to ask Kakashi to kick Naruto out. Naruto, feeling betrayed, leaves the village for a while to train hard and come back as a more mature and powerful ninja.
Perhaps Naruto's uncontrollable use of the Nine - Tails' chakra endangers the team during a mission. The village leaders see this as a huge risk and order him to be removed from Team 7. Naruto then embarks on a journey to better control his chakra on his own. He might meet some new friends or mentors along the way who help him become stronger and more in control, and eventually, he tries to make his way back to Team 7.
The villagers themselves could be the antagonists in a sense. They have always been somewhat afraid and resentful of Naruto because of the Nine - Tails. Their constant negative attitude towards Naruto could influence the decision to kick him out of Team 7. They might pressure the village elders and Kakashi into believing that Naruto is not a suitable member for the team and that he poses a threat to the safety of the other team members.
Maybe he was blamed for some trouble he didn't actually cause. For example, if something went missing in the orphanage and the caretakers wrongly thought Naruto took it.
One possible reason could be his unruly behavior. Naruto is known to be a bit of a troublemaker in the series, always pulling pranks. In fanfiction, this might be exaggerated, and the orphanage might not be able to handle it anymore. Another reason could be that he's suspected of being involved in something dangerous or illegal, even if he's innocent. For example, if there are strange incidents around the orphanage and Naruto is the easy target to blame because of his reputation.
One possible reason could be his prankster nature. Maybe he played one too many harmless but annoying pranks on the staff or other orphans, and they decided they'd had enough. Another reason might be the fear of the Nine - Tails within him. Even if the people in the orphanage didn't fully understand what it was, they could sense something dangerous about Naruto and wanted to distance themselves from him for safety reasons.
Well, perhaps one person in the threesome realizes they have strong feelings for only one of the other two and their jealousy causes them to act out in a way that leads to them being kicked out.
One possible reason could be a misunderstanding. Maybe there was a miscommunication during a mission, and the other members of Team Natsu thought Lucy made a big mistake. For example, if she accidentally led the enemy to their hiding place. Another reason might be jealousy. If Lucy's celestial spirit magic started to gain too much attention and overshadowed the others in some way, they could have decided to kick her out. However, this is all just speculation based on the idea of this fanfiction scenario.
One possible plot could be that Naruto is forced to leave Team 7 due to false accusations against him. Sasuke might then go on a solo mission to prove Naruto's innocence. Sakura, feeling guilty for not standing up for Naruto, decides to train harder to be able to bring Naruto back. And Kakashi, caught between the village's decision and his loyalty to Naruto, tries to find a way to reverse the situation.
Maybe he violated some important team rules. For example, he might have gone against the orders of the team leader during a crucial mission.
In a 'royal family kicked out' novel, the plot could revolve around a power struggle. There might be a powerful rival faction within the kingdom, either from the nobility or an emerging political group. They manage to oust the royal family through political maneuvers and intrigue. The displaced royals would then be on a journey to regain their power, facing numerous obstacles and making new alliances along the way.
Well, it could be about Naruto leading a team on a dangerous mission. Maybe they are sent to infiltrate a hidden enemy base. Naruto, with his experience and skills, guides the team through various traps and challenges. Along the way, they might face off against powerful ninjas and have to use their combined jutsus to survive.