Perhaps Naruto meets Raiden during a strange encounter in a limbo - like space. Raiden's calm and stoic demeanor might intrigue Naruto. Naruto, being a character who values growth and learning, would start to admire Raiden. He could then seek to learn from Raiden about leadership, as Raiden has experience leading his people. This admiration could be the basis for Naruto becoming a Raiden fan in the fanfiction.
In a fanfiction, Naruto could be exposed to a new form of chakra or energy similar to Raiden's electricity - based powers. This exposure could lead him to study Raiden's combat style. For example, Raiden's ability to move at high speeds and his proficiency with a sword could inspire Naruto to incorporate new techniques into his own fighting repertoire, thus making him a Raiden fan.
One way could be through Naruto's admiration for Kisuke's unique skills. Maybe Naruto discovers Kisuke's swordsmanship or his knowledge of spiritual energy. He then starts to study Kisuke's ways, trying to incorporate some of his techniques into his own fighting style. This would lead to Naruto changing his combat approach and even his way of thinking about battles.
One way could be through a strange crossover event. Maybe Naruto gets sucked into the Bleach universe and is somehow influenced by the power and allure of the Espada. He could start to adapt their fighting styles, for example, learning from their use of reiatsu and zanpakuto - like abilities. This would change his approach to battles in the Naruto world when he eventually returns.
One way could be through a time - travel or dimension - hopping plot device. Maybe Naruto gets sent to the Mega Man universe and is immediately fascinated by the high - tech world and Mega Man's heroic deeds. He starts learning about the different robots and their functions, and decides to become a fan. Another idea is that some kind of crossover event occurs in Naruto's own world. For example, a strange artifact is discovered that contains knowledge of the Mega Man universe, and Naruto, being the curious ninja he is, delves into it and becomes a fan.
Well, one way could be Sonic discovers Batman's comics in his world. Maybe Tails finds some strange artifacts that turn out to be from another dimension where Batman exists. Sonic reads the comics and is intrigued by Batman's determination and his no - kill rule. He starts to idolize Batman and tries to incorporate some of Batman's detective skills into his own adventures.
If Naruto becomes a Pokemon fanfiction, it could go like this. Naruto, being his curious self, would be intrigued by the concept of Pokemon. He might meet some Pokemon trainers who teach him the ropes. His natural leadership skills would help him in leading his Pokemon team. He could also bring some of his ninja tools and incorporate them into his Pokemon training and battles. For instance, using his kunai to mark the location of wild Pokemon. His journey would be filled with new adventures, making friends with other trainers, and learning about the different regions in the Pokemon world.
His view of the world might change. Raiden is often associated with protecting a larger realm, while Naruto has mainly focused on his village. As a Raiden fan, Naruto could start to think more about the broader world and his role in it, perhaps taking on more responsibilities outside of Konoha and developing a more global perspective.
One way could be to show Naruto's struggle with the illness while still trying to protect the village. He might have to train his friends to take over his duties in case he gets too sick.
Well, one way it could work is if Naruto's world somehow got merged with the dark and chaotic world of the Joker. Maybe Naruto, after facing so much pain and loss in his own world, starts to adopt the Joker's nihilistic views. He could use his ninja skills in a more unhinged way, like the Joker uses his chaos-creating abilities.
One way could be by combining Naruto's ninja abilities with Jedi powers. Naruto's chakra control could be related to a Jedi's Force control. For example, his Rasengan could be like a Jedi's unique Force technique. Also, Naruto's strong will, which is similar to a Jedi's determination in the light side of the Force, could play a major role in leading the Jedi Order.
One way this could be developed is by having Naruto's abilities misused or corrupted in the Hellsing universe. Maybe some dark magic or experiment twists his chakra into a force that creates 'monsters'. For example, his shadow clone jutsu could be warped so that the clones turn into uncontrollable, monstrous entities. Another aspect could be his connection to the Nine - Tails. If the Hellsing organization were to try and harness the power of the Nine - Tails, it could go horribly wrong and lead to the creation of new and terrifying monsters.