His powers would likely be enhanced to a godlike level. For example, his Rasengan might be able to destroy entire landscapes with a single throw. His speed could be so great that he appears to teleport. His chakra reserves would be seemingly infinite, allowing him to spam powerful jutsus without getting tired.
His ninjutsu might be enhanced by the magic in the Fairy Tail world. For example, his Shadow Clone Jutsu could have a magical aspect, like leaving behind a trail of magic energy. His Rasengan could also be powered up by the ambient magic, making it even more destructive.
Rias's power of destruction might be able to be enhanced by Naruto's Sage Mode. In Sage Mode, Naruto has enhanced perception and power. He could help Rias focus her destruction power more precisely, perhaps by using his Sage Mode to sense the weak points of their enemies and then guiding Rias to direct her power there.
Well, in this fanfiction scenario, Naruto's Nine - Tails chakra could blend with Rias's devilish powers. The Nine - Tails' raw power might be tamed and refined by Rias's more controlled and strategic devil abilities. On the other hand, Rias could use Naruto's chakra control techniques to better manage her own power. Their combined powers would not only make them a formidable couple in battle but also could potentially change the balance of power in both the ninja world and the devil world.
Well, Naruto's ability to sense things could change completely. His machine parts could be equipped with advanced sensors. For example, he could detect hidden traps or enemies from much further away. He might also be able to interface with other mechanical devices. If there were some sort of mechanical security system in a building, he could hack into it using his own machine components. And his Nine - Tails chakra might interact with the machine parts in unexpected ways. Maybe the energy from the Nine - Tails could power up his mechanical functions even more, or the machine parts could help him control the Nine - Tails chakra more precisely.
His powers might be more understated as a vigilante. Instead of using his flashy jutsus openly, he could develop more stealth - based techniques. For example, he might modify his Rasengan to be a silent and more deadly attack for surprise attacks on criminals.
His chakra could be used to power up the mechas in unique ways. For instance, instead of relying solely on the mecha's normal energy sources, Naruto could infuse his chakra into the mecha's systems to enhance its speed, strength, or weapon capabilities.
Naruto's powers could complement the members of Rias' peerage. For example, his speed could assist in quickly getting into position during battles, which would work well with the more long - range or support - based abilities of some peerage members.
Naruto's powers would be a game - changer. His Rasengan alone could be a very powerful weapon against the enemies in the devil world. His shadow clones could be used for various purposes, like scouting or overwhelming opponents in battle. This would give Rias' side a huge advantage in any conflicts.
Naruto could gain the power of mind control, similar to how Sauron could influence the minds of others. This would be a huge change for Naruto as he is usually all about friendship and persuasion through positive means. Now, he would have to struggle with this new power that goes against his normal moral code and figure out how to use it for good, if possible.
Naruto's powers are mainly based on chakra, which he can use for various ninja techniques like the Rasengan and Shadow Clones. Rias has her demonic powers and magic. In a fanfiction, their powers could combine in a very interesting way. For example, Naruto could use his chakra control to enhance Rias's magic spells. His ability to create a large number of clones could also be used in battles in Rias's world, where they could act as decoys or perform coordinated attacks with Rias's minions. Rias, in turn, could use her magic to enhance Naruto's physical abilities further, making his already powerful punches and kicks even more devastating.