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.
Well, it might be a very complex fanfiction. Naruto, being a character from a world of ninjas, and Sosuke Aizen from a world of Soul Reapers. In this fanfiction, Naruto could be reimagined as having Aizen's ability to deceive. He might use his shadow clone jutsu in new and devious ways, like Aizen uses his illusions. The story could also involve Naruto trying to take over a new kind of ninja world with Aizen - like strategies, all while his friends try to figure out what has happened to him.
First, understand Aizen's character traits thoroughly. He's manipulative, intelligent, and power - hungry. In a crossover, you need to show how these traits interact with the new world. For example, if crossing with 'Game of Thrones', his manipulation would be a great asset. He could play the different houses against each other. Second, give him clear goals. If it's a crossover with 'One Piece', his goal could be to find the One Piece and use it to rule the new world. Third, let his actions have consequences. If he makes a wrong move in a world like 'Naruto', the ninja might catch on to his schemes and fight back.
One idea could be a crossover with the 'Harry Potter' universe. Sosuke Aizen could be a dark wizard who infiltrates Hogwarts, using his charm and manipulation skills. He might try to sway students to his side, believing they can help him achieve his goals. Another idea is a crossover with 'The Lord of the Rings'. Aizen could be a powerful being in Middle - earth, perhaps using the One Ring for his own purposes if he got his hands on it. He'd likely deceive those around him to gain more power.
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.