A great plot idea is if the reincarnated character has a special power that the ninja world wants to control. They then have to go on the run while also trying to figure out how to use their power for good. Also, they could be reincarnated into the past of the Naruto world, before the main story events. This would allow them to change the course of history, like preventing the Uchiha massacre. Or perhaps they are reincarnated as a member of a secret organization that has ties to the origin of chakra, and they have to uncover the secrets while staying alive.
One plot idea could be that the reincarnated character has knowledge of future events in the Naruto story. They could use this knowledge to try and prevent tragedies, like the death of certain characters. Another idea is that they are reincarnated as a villain from their past life and have to struggle with their old evil tendencies while in the Naruto world. Or they could be reincarnated into a completely different body, like an animal, and have to find a way to become a ninja in that form.
One idea could be that the reincarnated character has knowledge of future events in the Naruto world. For example, they know about the Akatsuki's true intentions from the start and can start preparing the Hidden Leaf Village earlier. Another plot could be that they have a special power from their past life that no one in the Naruto world has seen before, like the ability to control modern technology within the ninja world. A third idea is that they are reincarnated as a side character and their actions end up changing the entire course of the original Naruto story in unexpected ways.
A plot could also involve Naruto being reincarnated at a different point in the Naruto timeline. For example, if he was reincarnated during the time of the Sage of Six Paths. He could have a major impact on the early development of ninjutsu and the ninja world.
A cool plot could be Naruto being reincarnated as an enemy of Konoha in a parallel universe. He has all his memories but has to fight against his former friends and home. This would lead to a lot of internal conflict for him. Also, he could be reincarnated into a time where there are new and strange forms of chakra that he has to learn to master in order to save the world again. For example, a chakra that is a combination of nature and spiritual energy.
Another good one is 'Reincarnated Naruto: The Legend Reborn'. In this fanfiction, Naruto's reincarnation brings a whole new set of challenges as he has to deal with different power structures. It also delves deep into his past life memories and how they influence his new life decisions. There are some really exciting battles in it.
The plot could revolve around Broly's reincarnation trying to find his place in the ninja world. He might start off as an outcast because of his strange powers. As he tries to fit in, he could get involved in the conflicts between villages. For example, he might be caught in the middle of a war between Konoha and Sand. His Saiyan power could be a key factor in turning the tide of battles.
Perhaps the reincarnated character has a special ability that allows them to communicate with the unique monsters in the Tensura world. This ability could lead to forming alliances that no one else could, and they could use these to their advantage to gain power and protect the world from new threats.
One idea could be that the oc retains some memories of their past life. So they use their knowledge to change things in the pjs world. For example, they might know of a coming danger and work to prevent it.
One idea could be that the reincarnated character has memories of the future of the Boruto world. So they try to prevent certain disasters from happening, like the fall of Konoha. Another could be that they use their modern - day knowledge to revolutionize the ninja technology in the Boruto universe.
One idea could be that the reincarnated character has knowledge of future events in the Danmachi world. For example, they know about certain monsters' weaknesses or hidden treasures. This could give them an edge as they navigate the dungeon. Another could be that they are reincarnated as a non - human race in the Danmachi world, like a spirit or a dwarf, and they have to deal with the different cultural and physical aspects of that race. A third idea is that the character reincarnates with a special ability that doesn't exist in the normal Danmachi world, like the power to control time on a small scale, which would completely change their adventures in the dungeon.
One idea could be that the protagonist, reincarnated as a dinosaur, tries to prevent the extinction event. They could use their human knowledge to find a way to survive the impending asteroid or environmental changes.