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.
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.
Naruto would probably become more interested in technology. In the original Naruto series, he doesn't really deal with high - tech stuff much. But if he becomes a Mega Man fan, he might start trying to incorporate some technological elements into his ninja tools or fighting style. For example, he could try to make a shuriken launcher inspired by Mega Man's weapons.
He'd become more responsible for the whole world perhaps. Since the Avatar has to keep balance everywhere.
He could become less impulsive. Seeing Himawari's more calculated and careful approach to things, Naruto might learn from her. He may start to think things through more before acting, just like he admires in Himawari. Also, he would be more of a cheerleader for her, boosting her confidence which in turn would change his own character to be more of an encourager in general.
If Naruto becomes a Jigsaw fan in fanfiction, his relationships would change drastically. His friends and comrades in Konoha would be confused and concerned. They have always known Naruto as a kind - hearted and positive person. His newfound interest in Jigsaw's ways would seem out of character. For instance, his bond with Hinata would be severely tested. Hinata, who loves Naruto for his heroic and gentle nature, would be at a loss on how to deal with this new, darker Naruto. His relationships with the other ninja clans in the village would also become tense as they would view his new ideology as a threat to the village's peace and stability.
Naruto's character would likely become more patient. Dealing with Pokemon, which are different from his usual ninja foes, would require a different approach. He would have to understand their behaviors and needs, which would make him more patient and empathetic. Also, his leadership skills from the Naruto series would be enhanced as he might lead groups of Pokemon trainers in this fanfiction world.
Naruto's character would gain a new sense of responsibility. As a Green Lantern, he'd have to abide by the Corps' rules and uphold justice on a much larger scale. This might make him more serious at times, but his core of being a fun - loving and determined person would still remain. He'd also learn to work in a team with other Green Lanterns, which could be different from his experience with his ninja teams as they come from diverse backgrounds.
He'd become more cynical. Naruto is known for his positive outlook, but as a gangster, he'd see the world in a darker light. His trust in others would be severely diminished.
Well, without reading it specifically, it could be about Naruto in a scenario where he becomes the champion in a context related to Raiden. Maybe it involves Naruto facing challenges in a Raiden - inspired world or having to prove himself worthy of some sort of Raiden - related title. It could also potentially involve Naruto using powers or abilities associated with Raiden.
Naruto's optimistic and energetic personality would contrast with Raiden's more reserved and serious nature. Naruto would likely be excited to learn from Raiden and would be constantly asking questions. Raiden, in response, would be patient with Naruto and start to open up more as he sees Naruto's good heart. Naruto's ability to inspire others could also have an impact on Raiden, making him more in touch with his emotions.