It might be a shadow - dragon. This type of dragon could give Naruto abilities related to stealth and the manipulation of shadows. It would be a very unique addition to his power set and could lead to some really cool fight scenes in the fanfiction.
Maybe it's an ice - dragon. This would be an interesting contrast to Naruto's usual warm - hearted personality. The ice - dragon's power could be used in creative ways in battles, like freezing opponents or creating ice - based defenses.
Well, it could greatly enhance his physical strength. With a dragon's power, Naruto might be able to deliver more powerful punches and kicks. His speed could also increase as the dragon's energy might boost his reflexes. And his chakra, which is already quite strong, could be amplified to new levels, allowing him to perform more powerful jutsus with ease.
It could be from an ancient and forgotten clan. Maybe a clan that had the power to tame and seal dragons long ago, and for some reason, they chose Naruto as the vessel for this dragon. Another possibility is that it came from a different dimension where dragons are common, and through some magical accident or ritual, the dragon ended up sealed in Naruto.
Maybe it would be an ice - dragon. This would be an interesting contrast to Naruto's usual warm - natured self. The ice - dragon could have blue - white scales and the ability to freeze things with its breath. It could also create ice - bridges or walls in battles, providing a unique strategic advantage for Naruto.
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.
The zanpakuto could have the power to breathe fire, just like a dragon. This would add a new offensive ability to Naruto's arsenal. He could use it in combination with his existing jutsu, like sending out a stream of fire while using his shadow clones to surround the enemy.
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.
Naruto might be able to create cloud - based illusions. Just as he can create shadow clones, with the power of Cloud sealed in him, he could project illusions made of clouds to deceive his opponents. These illusions could be large - scale and very realistic, confusing enemies about his true location and intentions.
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.
The addition of a dragon sealed in Naruto would be a huge game - changer. Naruto is already a complex character with the Nine - Tails, but a dragon would add another layer. His growth as a ninja would be different. He might face more discrimination due to the even more dangerous power he holds. In terms of the overall story, it could introduce new arcs related to the dragon's history and purpose. For example, there could be a group trying to free the dragon for their own evil purposes, and Naruto would have to stop them while also learning to master the dragon's power.
He might gain Minato's teleportation jutsu. It was one of Minato's signature moves, and with Minato sealed in him, Naruto could potentially access and learn this powerful technique.