The plot could start with Naruto somehow being transported to Aizen's world. He quickly realizes the danger Aizen poses. Naruto begins to train and adapt to the new environment, learning about reiatsu. As he battles minor foes related to Aizen, he gains knowledge about Aizen's weaknesses. Eventually, when facing Aizen, he uses his ninja skills and new - found understanding of this different power system to land a fatal blow.
Well, in a fanfiction scenario, Naruto might kill Aizen if he manages to use his shadow clones to outwit Aizen's illusions. Naruto could also use his Sage Mode to sense Aizen's reiatsu and counter his attacks. Maybe he combines his Rasengan with some new jutsu he's developed specifically to deal with Aizen's powers.
There could be. Given the creativity of fanfiction writers, it's not at all surprising that someone might come up with a concept where Naruto has some sort of connection to Sosuke Aizen. It might be a story where Naruto, with his ninja skills, encounters Aizen's devious plans and tries to thwart them, or perhaps a more complex story where their powers merge in some strange way.
The Soul Reapers would be very confused at first. They are used to Aizen being a certain way, and Naruto's different personality would be a shock. Ichigo might be curious and see Naruto - Aizen as an ally against the common enemies. Orihime could be one of the first to trust Naruto - Aizen because of his kind - hearted nature that she would sense. And the Espadas would probably be on high alert, not knowing what to expect from this new Aizen.
They might have a mentor - student relationship. Aizen, with his vast knowledge and power, would be in the position of a mentor, guiding Naruto. Naruto, being eager to learn and grow stronger, would be the student. However, there could be some tension as Naruto has his own sense of justice which might conflict with Aizen's more self - serving motives at times.
Naruto would probably be very cautious around Aizen at first. He's used to facing powerful enemies, but Aizen's deceptive nature would be a new challenge. Aizen, on the other hand, might see Naruto as an interesting specimen, someone with a strong will and great power that he could potentially manipulate.
Another idea is that Aizen somehow ends up in the Naruto universe during the time of the Fourth Great Ninja War. He could try to manipulate both sides for his own gain. But Naruto, with his ability to see the good in people, might try to reason with Aizen and show him a different path. It could be a story of redemption or a great battle if Aizen refuses.
Yes, there are some out there. You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Naruto is an Aizen fanfiction' in their search bars. Some stories might combine the unique powers and personalities of Naruto and Aizen in really interesting ways, like Naruto having some of Aizen's deceptive intelligence while still maintaining his own ninja values.
Sasuke could be a potential successor. He already has a thirst for power and a certain level of cunning. If he were to come across some sort of strange power source that gave him Aizen - like abilities, it would be an interesting twist. He could use his Sharingan in combination with new illusions and mind - control powers.
The plot could involve this successor being an outcast at first. Since their powers are so different from the regular chakra - based abilities in Naruto. But as they grow in power, they attract the attention of both villains and heroes. Villains might want to use them, while heroes try to stop them from causing chaos. For example, they could create clones that are indistinguishable from the real people, causing all sorts of mayhem in the villages.