He might gain a more powerful form of Rasengan, like a Rasengan that can change its shape and properties according to the situation. Maybe he has better control over his Nine - Tails chakra and can use it in more creative ways without losing control.
Naruto could potentially have unlocked a new type of elemental combination. For example, combining wind and lightning elements in a unique jutsu. He may also have developed a special ability related to his Uzumaki heritage, something that was previously dormant. Another possibility is that he has learned to use his chakra in a more efficient and powerful way, allowing him to perform stronger attacks with less effort.
In this fanfiction, Naruto could gain the power to sense and manipulate natural energy more effectively. This would enhance his sage mode abilities. He might also have the ability to transfer his chakra to others in a more efficient way, enabling him to heal or boost the power of his comrades. Additionally, he could have developed a new form of teleportation jutsu based on his understanding of space - time ninjutsu, though it would be less powerful than the likes of Kamui but still useful in combat and travel.
Naruto could potentially gain the power of mind - reading magic. This would be a huge advantage in both the wizarding war and in his interactions within Konoha. He could also gain the ability to transform into magical creatures, which would give him new forms of attack and defense. Another possibility is that he gains the power to nullify magic, which would make him a key player in the fight against wizards who use dark magic.
Naruto would gain some really cool (pun intended) new abilities. The ice - making ability would be the most prominent. He could form ice clones, similar to his shadow clones but with the added advantage of being made of ice and potentially having more durability. His sensory abilities might also be enhanced, as Esdeath has a good sense of her surroundings when using her powers. He could detect enemies hidden in the ice or snow. And, like I said before, the time - freezing power. This would allow him to analyze his opponents' moves during the frozen time and come up with the perfect counter - attack. It would add a whole new dimension to his combat skills.
Well, considering the devilish nature of Rias' world, Naruto could gain the power of flight, which is not something he has in his original ninja world. He could also gain the power to resist holy attacks, as devils are often weak against holy elements. Another power could be the ability to create and control demonic flames. These new powers would not only change his combat capabilities but also how he is perceived in this new fanfiction world.
He might gain enhanced physical strength like Bane. Bane was known for his brute force, so Naruto could have a similar boost, being able to overpower his opponents more easily in hand - to - hand combat.
Well, Naruto could also gain some sort of enhanced perception. The Juubi has a connection to all things in the Naruto universe in a way. So, by holding it, Naruto might be able to sense things from much farther away, like threats or allies in need. This would give him a huge advantage in battles and also in his role as a protector of the village. He could react faster to any incoming danger.
Naruto could gain enhanced senses from the Ghost Rider powers. In the Naruto world, this would help him in detecting hidden enemies or traps more easily. The ability to ride the flaming motorcycle would also be a new skill. This could be used for quick transportation during missions or battles. He could also gain the power of transformation into the Ghost Rider form, which not only gives him a more intimidating look but also access to all the other Ghost Rider abilities. And with the Ghost Rider's connection to the spirit world, Naruto might be able to communicate with spirits in the Naruto universe, which could lead to new plot developments.
He might gain some of Madara's Sharingan - related abilities. Maybe he could use some of the advanced genjutsu techniques that Madara was proficient in. Since Madara had strong chakra, Naruto could also potentially have an increase in his own chakra levels or a new way to manipulate chakra, like Madara's ability to control the Susanoo.
He could gain the power of controlling water like Poseidon's kids since he has good chakra control. It would be a new addition to his skill set.
He could gain super strength, allowing him to overpower enemies more easily than before. His speed would be enhanced to a level that might make him almost impossible to catch. And he could have the power of hypnosis, which would be useful in combat and getting information from foes.
Well, Naruto could gain the ability to heal in a more advanced way. Just as the avatar can sometimes use their connection to the elements to heal, Naruto might be able to do the same with his chakra. He could also have the power to merge with the natural world around him, similar to how the avatar can connect with nature. This would give him an edge in stealth and surprise attacks. Plus, he could develop a new form of sensing, being able to detect not just chakra but also the energy of the elements around him.