One possibility is that Naruto's reincarnation as Aizen would lead to a whole new set of battles. He might face off against some of the powerful Hollows or even the more powerful Soul Reapers who see him as a threat. His Naruto - based powers could be a huge advantage in combat. He could use his chakra control to enhance his sword skills or his ability to sense spiritual pressure. And his journey through the Bleach world as Aizen could be about finding a way to bring peace, just like he always aimed for in the Naruto world.
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.
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.
Perhaps the fanfiction could revolve around Aizen being a fan of Naruto's never - give - up attitude. So he decides to travel to the Naruto world to learn from Naruto. In this story, Aizen could start off as an antagonist - like figure but gradually become inspired by Naruto and change his ways. It would be an interesting take on how two very different characters from different universes could influence each other.
One possible plot could be that a powerful villain tries to create a new Buu - like being using Naruto's chakra. But instead of creating a new Buu, Naruto is reincarnated as a hybrid of himself and Buu. This would lead to a lot of internal struggle for Naruto. He would have to deal with Buu's instincts while still trying to protect his village and friends. His friends might be initially scared of him, but over time they come to understand and accept this new Naruto.
The fanfiction could have a plot where Obito's reincarnation is not a normal one. He is reincarnated with a special mission from the afterlife. He has to find a way to bring peace to the shinobi world in a different way than Naruto did. He might have to face new enemies and also deal with the old grudges that still exist among the ninja clans. His reincarnation could also bring about a change in the relationship between the different villages as he tries to use his past experiences to create a more united and peaceful ninja world.
Maybe Naruto would have some of Ichigo's powers. For example, he could have a zanpakuto instead of a kunai.
In this fanfiction, perhaps Naruto is the reincarnation of Alucard due to some ancient prophecy. His journey would then be about discovering his connection to Alucard. He could start having strange dreams about Alucard's past life and battles. As he uncovers more, he realizes he has to use Alucard's powers to save the ninja world from a new, powerful threat that only his combined Naruto and Alucard abilities can defeat.
Perhaps the story could start with Naruto having strange dreams about Goku's life. As the story progresses, he gradually unlocks Goku's powers. He could then use these powers to protect the Hidden Leaf Village in a more powerful way. For instance, when the village is under attack by a powerful enemy, Naruto could transform into a Super Saiyan - like state, shocking his enemies and allies alike. His training would also change, as he'd have to learn to control his new Saiyan powers, which would be a whole new journey for him.
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, one possible plot could be that Naruto, through some sort of interdimensional rift or magic, gets to witness Aizen's power in the Bleach universe. He is so impressed by Aizen's strength and his ability to manipulate those around him that he becomes a fan. Then Naruto might try to learn some of Aizen's strategic thinking to use in his own battles in the Naruto world.