He might become more confident, bordering on overconfident at times. The power of the Juubi could make him feel invincible.
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.
His personality might become more assertive. The power of the Juubi could make Naruto more confident in his actions and decisions. He may be less hesitant to use force when necessary.
His personality might become more intense. The Juubi's power could make him more assertive. He might be less hesitant in making tough decisions.
Well, he would probably become extremely powerful. His already impressive chakra reserves would be multiplied many times over with the Juubi's power. He might gain new and unique jutsu that are a combination of his own and the Juubi's abilities.
Well, when Naruto absorbs the Juubi in a crossover fanfiction, his appearance would be a visual representation of his new power. He could have some sort of chakra horns or spikes protruding from his body, similar to some of the forms of the tailed beasts. His eyes might become more slitted and have a more menacing look. The overall look would be a blend of Naruto's original appearance and the terrifying and powerful essence of the Juubi, making him look both familiar and yet completely different at the same time.
His relationship with Sasuke would be very different. Sasuke might see Naruto as a threat at first, given the power of the Juubi. But eventually, they could come to an understanding. Naruto would still want to protect Sasuke, and Sasuke might realize that Naruto's intentions are pure even in his Juubi form.
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.
If Naruto were on Team 8 in fanfiction, his personality could develop in several ways. He may become more empathetic as he gets to know his new teammates better. Hinata's shyness might make him more sensitive to others' feelings, and he would try to encourage her more. Also, being around Shino's quiet and methodical nature could make him more reflective. He might start thinking more about the consequences of his actions before acting, which is a big change from his usual impulsive self. He could also become more competitive in a different way, trying to prove himself not just in combat but also in the more specialized skills that Team 8 values, like tracking and espionage.
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.
Well, Naruto's personality would have an interesting transformation. He would likely become more of a risk - taker. The pirate world is full of uncertainties and dangers, and Naruto would embrace this. He might become more laid - back in some ways, enjoying the simple pleasures of life at sea like drinking grog (if they have something similar in this fanfiction world) and singing sea shanties. But at the same time, his competitive nature would still be there. He'd want to prove himself as a great pirate, perhaps competing with other well - known pirates. His naivete might also change a bit. While he was often naive in the ninja world, the harshness of the pirate life would make him more street - smart, yet still retain his positive outlook on life.