Well, it could be that Naruto is really confused at first. He might find the ideas in the fanfiction very strange, like the new powers of immortality described. Maybe he starts to question his own understanding of the ninja world.
Perhaps in this 'naruto reading the first immortal fanfiction' scenario, the fanfiction is actually a prophecy in disguise. Naruto, not realizing it at first, starts to notice that some of the events in the fanfiction seem to be related to things that are starting to happen in the real ninja world. He then feels a sense of urgency to understand the rest of the fanfiction to prevent any disasters or to bring about a new era of peace. He might go on a journey to find the author of the fanfiction, believing that they have some kind of special knowledge or power.
Well, in this fanfiction, Naruto's immortality could lead to him being a sort of legend in the Pokemon world. He might start a new ninja - Pokemon fighting style. He'd use his shadow clones to train multiple Pokemon at once. And his immortality would mean he could face any danger in the Pokemon world without fear of death. This could attract the attention of the Pokemon League, who would be both intrigued and a bit worried about this new and powerful trainer.
In the 'naruto is an immortal child fanfiction', it could be that Naruto's immortality is a curse rather than a blessing. He is forever trapped in a child's body, unable to fully experience adult life. He might struggle with his identity as he is different from everyone else. He could then embark on a journey to find a way to either end his immortality or find a purpose for his eternal existence.
The plot might involve Naruto trying to find a way back to his own universe while getting involved in the affairs of the DC Universe. He could use his ninjutsu to fight against supervillains. Also, his immortality would give him an edge in long - drawn battles and he could form interesting relationships with DC characters like Batman, who might be intrigued by his abilities.
Well, perhaps Naruto, with his immortality, would bring his ninja skills to Hogwarts. He might teach the students some unique combat moves, or get involved in battles against dark wizards using his Rasengan and shadow clone techniques.
Well, one possibility could be that Naruto somehow gets transported to the DC universe where the Immortal Justice League exists. Maybe he teams up with them to fight a common enemy like Darkseid or some other powerful villain. Naruto's unique jutsu and combat skills would add a new dynamic to the League's battles.
Another plot twist might be that Naruto reads a future where the entire ninja world is in ruins. This could lead him to take extreme measures in the present to prevent that future from happening. He might try to unite all the ninja villages in a way that has never been done before, facing many obstacles along the way as different villages have their own interests and grudges.
One possible plot could be Hoke reincarnating as an unknown ninja in a small village. He then starts to show extraordinary abilities which draw the attention of the major ninja villages. Along the way, he befriends Naruto and the gang. He might teach them some new techniques that he remembers from his previous life. He could also get involved in the Akatsuki conflict, either trying to stop them in a different way or even trying to understand their motives from a different perspective.
The plot could be really interesting. Imagine Naruto, with his strong will and determination, being reborn as the first Hassan in the FGO world. He would have to learn the rules and magic of this new world. His ninja training and experiences in the Naruto world would give him an edge. He might encounter some FGO characters who are initially skeptical of him because he's so different. But as they see his power and his unique abilities like his Rasengan, they start to accept him. And then they all team up to face powerful foes that are emerging in the FGO world, and Naruto uses his Naruto - esque strategies and skills to turn the tide of the battles.
One possible plot could be that the first male born in a certain clan has some unique powers. For example, he might be able to control an element in a way that no one else in the clan can. He could be seen as a savior or a threat depending on the political situation within the Naruto world. His journey could involve training with the best ninjas, like Naruto himself, to master his powers and bring peace to his clan.
The plot could center around the first male ninja facing some great threat to the ninja world. He might be on a quest to find a powerful jutsu or artifact to save everyone. Along the way, he could encounter various challenges, make new friends and enemies, and his character could develop as he overcomes these difficulties. For example, he could start as a novice and gradually become a respected and powerful ninja.