Well, it could start with Naruto being exposed to some kind of media from the Mega Man world. Perhaps a traveling merchant brings in some strange device that can play videos of Mega Man's adventures. Naruto, always eager to learn about new things, watches these videos and is completely captivated by Mega Man's courage and the cool robotic battles. He then starts collecting any information he can about Mega Man, becoming a huge fan.
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.
If Naruto were to become a Mega Man fan in a fanfiction, it might be because he sees similarities between Mega Man's battles and his own as a ninja. Mega Man fights against powerful robotic enemies to save the world, and Naruto battles powerful foes to protect his village. This connection makes Naruto admire Mega Man. He might also be intrigued by the advanced technology in the Mega Man universe, which is so different from his own ninja - based world. So, he begins to follow Mega Man's adventures and becomes a 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.
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 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.
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.
Naruto's character could develop in many ways. He might become more strategic as he has to learn how to use Mega Man's powers effectively. His confidence could also grow even more, making him a more inspiring leader.
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.
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.
It could be about Naruto being transported into the Mega Man world and having to adapt to the new technology and challenges there. Maybe he uses his ninja skills in unique ways to fight the robotic enemies in the Mega Man universe.
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.