Well, it could mean that Naruto's actions become more mechanical. Without a soul, he might lack the emotional depth that drives his character in the original series. For example, his bonds with friends like Sasuke and Sakura would be very different, perhaps more of a logical alliance rather than the deep, soul - connected friendships we see in the original.
In a 'naruto has no soul' fanfiction, the plot would deviate significantly from the original. His growth as a ninja would be stunted in a way. His ability to learn new jutsu might be hampered because the understanding and connection that comes with having a soul are missing. His interactions with the Nine - Tailed Fox would also change. The fox might see him as a more empty vessel and either try to take over more easily or completely ignore him as he lacks the spiritual essence it used to battle against.
Yes, there are quite a few. You can check out fanfiction websites like FanFiction.net or Archive of Our Own. Some stories might explore Naruto's newfound soul magic abilities in relation to his existing ninja skills, like how it could enhance his Rasengan or his shadow clone jutsu.
It could be an ancient inheritance. Maybe Naruto is a descendant of a long - forgotten clan that had special soul powers, and these powers have been dormant in his bloodline until now.
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.
The soul power could be related to the Nine - Tails. Since the Nine - Tails is such a powerful entity within Naruto, his soul power might be a way to better control or even transform the Nine - Tails' power in a more positive and spiritual way. For example, instead of just using the Nine - Tails' chakra for brute strength, he could use his soul power to make the Nine - Tails' power more harmonious and less destructive.
Yes, there might be. Fanfiction websites are filled with all kinds of creative and unique crossovers. You can start by checking popular fanfiction platforms like FanFiction.net or Archive of Our Own. Just search for 'naruto is the soul king' and see what comes up.
His relationships would become more complex. The villagers who once hated him for having the Kyuubi inside him might now be even more terrified as he has its soul. However, Naruto's friends like Shikamaru would likely see this as an opportunity for Naruto to grow even stronger. They would try to help him harness this new power while also making sure he doesn't lose himself to the Kyuubi's wild nature. This new situation would test all of his relationships.
Maybe Naruto would sell his soul to a dark and mysterious ninja who has some sort of ultimate power or knowledge. This ninja could be using Naruto's soul for some grand, but evil, plan.