In a fanfiction with Naruto having Frieza sealed in him, there would be a clash of cultures too. Naruto comes from a world of ninjas with honor and teamwork, while Frieza is a tyrant from a universe where power rules all. Naruto would have to find a way to balance Frieza's power without losing his own values. His training would take a whole new turn as he tries to master Frieza's power. And there could be a lot of internal conflict as Naruto battles with Frieza's consciousness inside him, trying not to let Frieza take over his body.
The story could progress with Naruto facing new and more powerful enemies. With Frieza's power, he might attract the attention of stronger villains. His friends might also be in more danger as Naruto's new power makes him a bigger target.
I'm not entirely sure if there is a specific fanfiction with exactly that premise. However, given the popularity of both Naruto and the concept of sealing powerful entities in Naruto's world, it's quite possible. Fanfiction writers love to experiment with combining different fictional elements, so it wouldn't be surprising if someone has written a story where Jenova is sealed in Naruto. You can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own to find out for sure.
In many such fanfictions, it could be a variety of deities. It might be an ancient and powerful god from Naruto's world's mythology that the story's author has chosen to insert. For example, it could be a god of elements like a super - powerful fire god, which could give Naruto even more control over his existing fire - based jutsu and new, more extreme abilities related to fire.
With his enemies, it would be a whole different story. They might be more cautious about attacking Naruto. Some might even try to find a way to use the god sealed in him for their own purposes. And Naruto's relationship with the hidden villages could also change. They might see him as a potential threat or a very valuable asset.
Well, Naruto might become more mysterious. Since Gaster is an unknown and rather enigmatic entity, Naruto could start having strange thoughts or powers that he doesn't fully understand at first. He might seem more withdrawn as he tries to figure out what's going on inside him, and his normal cheerful and straightforward personality could be clouded by the presence of Gaster.
His abilities would change in multiple ways. Firstly, his chakra control might be affected. Since Godzilla is a massive and powerful entity, it could disrupt Naruto's normal chakra flow. However, he could also learn to harness Godzilla's power within him. For example, he might be able to use Godzilla's raw strength to enhance his Sage Mode or even his Nine - Tails transformation. This could make him an even more formidable opponent. His speed could also be enhanced as Godzilla's power might give him a boost in his physical capabilities, allowing him to move faster and react quicker in battle.
He could gain the power of manipulation. Gaster might give Naruto the ability to manipulate space or time on a small scale. Maybe he could create small portals or slow down time for a short period during combat.
In such a fanfiction, Naruto might gain some extraordinary powers related to the phoenix. For example, he could have the ability to heal quickly like the phoenix's regenerative powers. He may also be able to use fire - based attacks that are far more powerful and unique compared to his regular jutsu.
Well, one possibility could be that Naruto gains new powers related to the Nibi. He might be able to use some of its unique chakra abilities, like enhanced speed or stealth. Maybe he could also communicate with other Nibi - related things in the Naruto world.