Naruto could gain the ability to manipulate light and darkness, which are often associated with Keyblades. This would be a huge change from his normal chakra - based abilities. He could also use the Keyblade to fly, giving him an advantage in both mobility and combat. Another new ability might be the power to heal, as some Keyblades have restorative properties.
If Naruto got a Keyblade, he could gain the ability to transform. Keyblades often have different forms or upgrades. Naruto could transform his Keyblade into a more powerful version during intense battles. This would be similar to his Sage Mode or Nine - Tails Chakra Mode, but with a Keyblade twist. He could also gain the ability to create barriers using the Keyblade. These barriers could protect him and his allies from powerful attacks, and he could customize them according to the situation, like making them stronger against certain types of jutsu or attacks.
One new ability Naruto could gain is the power to communicate with hearts. In the world of Keyblades, understanding hearts is important. Naruto, who is already good at connecting with people on an emotional level, could use this to his advantage. He could sense the true intentions of his enemies or even calm down angry beasts. Additionally, the Keyblade might give him the ability to summon special creatures or entities that are linked to the Keyblade's power. This would add a whole new dimension to his battles and strategies.
He could potentially gain an enhanced understanding of wood - style techniques. Since Hashirama was a master of it, Naruto might learn how to create more complex and powerful wood constructs, like huge forests for both offense and defense.
The Sharingan might also give Naruto the ability to enter people's minds, at least to some extent. In the Naruto universe, the Sharingan has been shown to have some mind - related abilities. Naruto could use this to communicate with his friends in a more direct way, or perhaps even to break through genjutsu more easily. And, if he can enter the minds of his enemies, he could gather valuable information about their plans and weaknesses.
Naruto would gain the ability to copy jutsu. With the Sharingan, he could watch an opponent's movements closely and replicate their techniques. This would be a huge advantage for him in battles.
Naruto might gain the power of shikai and bankai. Shikai is the first release of a zanpakuto's power, and bankai is the ultimate form. Naruto, with his determination and strong will, would strive to master these forms. Shikai could give him new attacks and defenses, while bankai could make him an extremely powerful force. For example, his bankai could combine his ninjutsu skills with the zanpakuto's power in a unique and devastating way.
Well, Naruto might use the Keyblade to gain power and respect. He could start training with it and show those who neglected him what he's capable of.
Naruto would likely gain the ability to use all six paths techniques. The Rinnegan allows the user to manipulate gravity, as seen when Madara used it. Naruto could use this to enhance his combat skills, for example, pulling enemies towards him or pushing them away forcefully. He could also use the Preta Path to absorb chakra, which would be a great addition to his already large chakra reserves.
He could gain the ability to create large - scale wooden structures, like Hashirama did. For instance, he could build huge wooden golems to fight for him in battles.
Naruto could potentially gain the power of omnipotence. Since the Infinity Stones are extremely powerful in the Marvel universe, in the Naruto fanfiction, they could give Naruto abilities beyond imagination. He might be able to use the Stones together to rewrite the rules of the ninja world. For example, he could make chakra obsolete and introduce a new form of energy using the combined powers of the Stones. Also, he could use the Power Stone to boost the power of his Rasengan to an unimaginable level, capable of destroying entire mountains with a single throw.
He might gain enhanced chakra control. Since he has the Kyuubi's soul, he could have better access to the Kyuubi's chakra reserves and be able to manipulate it more precisely. Maybe he could also gain some of the Kyuubi's natural abilities like better senses, especially smell, which could help him in tracking enemies or finding things.
Another ability Naruto could gain is a deeper understanding of genjutsu. Shisui was very proficient in genjutsu, especially with his Sharingan. Naruto, being his brother, could have a natural aptitude for genjutsu. He could learn to break through stronger genjutsu more easily and also use more advanced genjutsu himself. This would be a significant change as Naruto was not originally known for his genjutsu skills, but with this new connection, he could become a more well - rounded ninja.