It could be a powerful rogue ninja who has made Zacks Island his lair. He might be hoarding some valuable resources on the island and sees Naruto as a threat to his plans.
Well, a great plot for a 'Naruto Zacks Island' fanfic could involve Naruto being sent to Zacks Island for a special training mission. On the island, he discovers an ancient prophecy related to his Nine - Tails power. He has to work with the local inhabitants, who are initially skeptical of him, to fulfill this prophecy and in the process, he learns new techniques and gains a deeper understanding of his own power.
A more complex fanfic could involve a portal opening between the Naruto universe and Dead Island. Some of the Dead Island survivors end up in the Naruto world and vice versa. The survivors are amazed by the ninja powers and try to learn some basic ninja techniques to defend themselves better. Meanwhile, the Naruto characters are intrigued by the technology and the situation in Dead Island. Naruto might even try to find a way to save the Dead Island world using his never - give - up attitude.
Perhaps Naruto will encounter some ancient spirits or deities that are native to the island. These entities could have their own agendas and might either help or hinder Naruto depending on how he interacts with them. Another possibility is that he meets some hermits who have been living on the island for a long time and have unique skills or knowledge that Naruto can learn from.
He could meet a lost shinobi from a different village. This shinobi might have been stranded there for a long time and has some valuable knowledge or skills that Naruto could learn from.
A lot of 'naruto jungle island fanfic' have themes related to teamwork. Naruto and his comrades need to work together to overcome the difficulties on the island. Also, there might be themes about the connection between nature and the ninja abilities. For example, how the unique environment of the jungle island affects their jutsu or chakra. There could also be themes of mystery, as the jungle island may hold many unknowns waiting to be uncovered.
He might have to figure out how to survive on his own. Maybe he'll start by looking for fresh water sources like springs or collect rainwater. He could also try to find food such as fishing in the island's waters or hunting small animals if there are any.
Another idea for the Naruto deserted island fanfic is that Naruto is sent to the island as a form of training. He initially struggles to adapt to the harsh environment. However, as time passes, he learns to control his chakra in new ways, perhaps by using the natural elements of the island. He could also meet a hermit on the island who teaches him some unique ninja techniques.
A possible plot for this fanfic could involve Naruto being teleported to a deserted island which has an abundance of lemon trees. As he tries to figure out how to get back home, he starts to experiment with the lemons. He might find that the lemons have some sort of energy that he can harness. This could attract the attention of some local island spirits or creatures. Naruto then has to use his ninja powers and the power of the lemons to either befriend or defeat these beings in order to find a way off the island.
Well, you can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. There might be some really interesting 'naruto jungle island fanfic' there. Just search for the specific tag or keyword and you'll likely find a bunch of stories to choose from.