The power balance would be greatly affected. If fanfiction gives Naruto some overpowered abilities like instant teleportation across any distance, it would make many of his battles much easier. Enemies that were once a threat would no longer be so.
The relationships in the Naruto universe could be rewritten. For example, if in the fanfiction Naruto has a different family background, his relationship with characters like Iruka or the Third Hokage could be very different. He might not have the same emotional connection to the village as he originally did.
The overall theme of the Naruto universe might shift. Fanfiction often explores different themes than the original work. If the fanfiction fused with Naruto is more about political intrigue, then the Naruto universe could become more focused on power struggles within the village and between different ninja clans rather than just the overarching themes of friendship and perseverance in the original Naruto.
Naruto would probably get Madara's Sharingan abilities. This could give him enhanced perception and the ability to copy jutsu more easily, like a supercharged version of his own ability. He might also gain access to Madara's Susanoo, which would be a huge boost to his combat capabilities.
It would change the combat dynamics a great deal. Guns are much more powerful in terms of long - range attacks compared to traditional ninja weapons. This would mean that strategies for battles, both in the village and against enemies, would need to be rethought. For instance, the importance of cover and stealth would increase significantly.
Well, Naruto getting a Keyblade would be a wild turn. Firstly, the Keyblade has a certain magic to it. Naruto's world is mainly about chakra, but with a Keyblade, he could introduce a new form of energy. He might be able to combine chakra with the power of the Keyblade. In terms of his friends, they would be both amazed and a bit envious. Sasuke, for instance, would see it as another way Naruto is getting stronger. And Naruto would have to learn how to wield it properly. He might start training with it in the same way he did with his rasengan, trying to master all its functions and forms.
The storylines would be more diverse. Instead of the typical ground - based adventures and battles, there could be more exploration of the skies and high - altitude regions. Also, Naruto's relationships with other characters might change. Some characters might be in awe of her wings and new abilities, while others might be envious. This could lead to new character arcs and development, like Sasuke seeing Naruto's wings as another sign of her growing power and feeling the need to become stronger himself.
It would change the power dynamics. With her succubus powers, fem Naruto could disrupt the traditional balance of strength. For instance, she might be able to defeat stronger opponents more easily by using her charm and allure.
His personality could become more calculating. Since Cell is a rather cunning and strategic being, Naruto might start to think more like a tactician. He'd still have his core values of protecting his friends and the village, but he'd approach battles with a different mindset.
He might become more confident, bordering on overconfident at times. The power of the Juubi could make him feel invincible.
If Naruto gains a Zanpakuto, it would completely change the power dynamics in the Naruto universe. Naruto is already extremely powerful with his chakra and Sage Mode, etc. A Zanpakuto would add a whole new dimension to his combat abilities. He might be able to use its unique powers in combination with his shadow clones, for example, sending clones out with the Zanpakuto's special abilities to surprise opponents. It could also potentially give him new ways to deal with different types of jutsu and enemies.
If Naruto had Quincy powers, his combat style would be drastically different. Quincy powers in 'Bleach' are mainly about manipulating spiritual energy in a very precise way. Naruto, who is used to his chakra-based techniques like Rasengan, would now have the ability to fire spiritual arrows or create constructs out of spiritual energy. This could potentially make him even more powerful in battles against the likes of Sasuke or the Akatsuki. His Sage Mode could also interact in interesting ways with the Quincy powers, perhaps enhancing the range and precision of his spiritual attacks.
Well, for starters, Naruto being a Sith Lord would mean a huge shift in the power balance. His chakra abilities combined with Sith powers would make him an extremely formidable foe. The Hidden Leaf Village would no longer be the same. It might turn into a place ruled by fear rather than the harmony it once had. His training would be different too, focusing more on dark side techniques rather than the traditional ninja training. And his appearance might even change to reflect his new dark status, perhaps with darker clothing and a more menacing look.