In the fanfiction, Harry Potter might gain the power of precise control. The Nuibari is known for its ability to stitch things together in the original Naruto context. So perhaps Harry could use it to 'stitch' spells together in a new and unique way, creating more powerful and complex incantations.
The fanfiction might change the plot in terms of Harry's relationships. Maybe his new ability with the Nuibari makes some of his friends jealous or in awe of him. Also, it could attract the attention of new characters or factions who are interested in the Nuibari. This could create new alliances or rivalries for Harry. For example, some dark wizards might want to steal the Nuibari from him, leading to new conflicts. And in his journey to master the Nuibari, he might have to visit new places or seek help from unexpected sources, thus diverging from the original plot.
The dragon sword might give Harry Potter enhanced combat abilities. It could potentially allow him to cut through dark magic defenses more easily, much like how the Sword of Gryffindor could destroy Horcruxes. Maybe it gives him the power to communicate with dragons, since it's a dragon sword, and use their strength in battles against Voldemort and his Death Eaters.
Harry might gain the ability to dodge attacks more easily. Sans has a certain 'instinct' for avoiding harm, and if Harry had this, it would be much harder for his enemies to land a hit on him. This would be really useful in duels, especially against powerful dark wizards. It could also make his Quidditch playing even more amazing as he could dodge bludgers effortlessly.
In this fanfiction, Harry Potter could obtain Gungnir in a rather unexpected way. For example, due to a time - traveling incident. He might accidentally travel to a different time and place where Gungnir exists. There, he could be in a situation where he has to help the local magical community. As a result of his heroic deeds, the keepers of Gungnir decide to entrust him with it. And when he returns to his own time, he brings Gungnir with him, ready to use it in his fight against the dark forces.
In this fanfiction, Harry could gain the power of enhanced perception. This would allow him to see things that normal humans or even wizards can't, such as the flow of spiritual energy. He might also gain the power to transform into a more powerful form, like a Shinigami's Bankai. His existing magical powers could potentially merge with his new Shinigami powers, creating something entirely unique. For instance, he could use his Patronus charm in a new way within the Shinigami world, perhaps as a form of spiritual protection.
He gains super - speed, of course. This allows him to move faster than any normal wizard. He can also vibrate his molecules to pass through solid objects, like walls in Hogwarts, which gives him a great advantage for sneaking around or escaping from tight spots.
Well, if Harry Potter has Deadpool's powers, he might become more carefree and irreverent. His traditional sense of duty could be tempered with Deadpool's chaotic nature. He could start cracking more jokes during dangerous situations, like when facing Voldemort. His attitude towards rules might change too, as Deadpool is not one to follow rules strictly.
It could have the ability to communicate with Harry on a psychic level. Telling him when danger is near or guiding him on how to use its powers most effectively in different situations.
He can sense the intentions of his enemies better. Haki allows him to perceive the hidden motives and attacks of dark wizards before they strike, giving him an edge in combat.
In a 'Naruto has Nuibari' fanfiction, the plot might involve Naruto accidentally coming into contact with Nuibari in a mysterious way. This weapon then starts to have an influence on his mind, showing him visions of past battles it was involved in. Naruto has to figure out how to control this connection and the power of Nuibari. As he does so, he realizes that there is a hidden secret about the weapon that is linked to his own family history. He then embarks on a journey to uncover the truth about Nuibari and his family, all while using the weapon to protect his village from threats that are starting to emerge because of his new - found power.