A plot could involve Naruto being cursed by an enemy. As a result, he can only consume food by using his whole body. At first, he's embarrassed and tries to hide it from his friends. But then he realizes that this new way of eating gives him an unexpected advantage in battle. For example, he can quickly consume a large amount of food to boost his energy during a fight.
Sakura would probably be both disgusted and amused at the same time. She might scold Naruto for being so unhygienic at first, but then laugh at his silly antics.
Yes, there might be some out there in the vast world of fanfiction, but it's likely a very dark and disturbing take on the Naruto universe. Most official Naruto stories don't have such elements as Naruto eating flesh. Fanfiction can sometimes explore extremely abnormal and unorthodox ideas, but this goes against the general positive and heroic image of Naruto in the original work.
It could enhance his teamwork. With the power of the Suna Suna no Mi, Naruto could create sand barriers to protect his team members during battles. His new ability would add another layer of defense and offense to their group strategies.
He might face some initial instability. His body could reject the changes at first, leading to things like loss of control over his movements or chakra.
It could either strengthen or strain their relationship. If Naruto gains power from the Shinju fruit and uses it for good, Sasuke might respect him more. However, if Naruto starts to change in a way that Sasuke doesn't like, it could cause friction. For example, if Naruto becomes too overconfident with his new power, Sasuke might see it as a negative change. Or, if Naruto's new power makes him a target, Sasuke could feel the need to protect him, which would bring them closer together in a different way than before.
His relationship with Sasuke might change. Sasuke is used to Naruto's regular abilities. But if Naruto had devil fruit powers, Sasuke might view him as an even greater rival or, in some cases, a potential threat. He could also be more intrigued by Naruto's new powers and be more likely to team up with him to face stronger enemies.
His training would change a lot. He'd have to learn to control the water powers from the fruit. Instead of just focusing on chakra training, he'd need to practice shaping water, like making it into different forms like animals or tools. Maybe he'd start training near water sources more often to get a better feel for his new powers.
Well, Naruto is obviously one of the main characters since it's in the title. He's the one doing all the eating. There might also be his friends like Sasuke and Sakura. Sasuke could be annoyed by Naruto's eating habits, while Sakura might be worried about the effects of all that eating on Naruto's health.
Perhaps in the 'naruto eats souls fanfiction', Naruto is cursed by an evil force. This curse makes him uncontrollably eat souls. He then has to struggle to find a way to break the curse while dealing with the consequences of having eaten souls, like the anger of the spirits' friends or families.