It depends on how the author writes it. But if Naruto has all his powers and the will to win, he could defeat the Juubi. He has shown amazing growth and power throughout the Naruto series.
Well, it could be that Naruto uses his new Sage of Six Paths powers to combat the Juubi. Maybe he has to find a way to break through the Juubi's defenses which are super strong. He might also get some help from his friends at some point in the fanfic.
Well, a 'naruto birth of the juubi fanfic' might be about the origin or the creation of the Juubi in the Naruto universe. It could explore how the Juubi came into existence, perhaps involving different chakra elements, ancient clans, or powerful jutsu that led to its birth.
If Naruto was the Juubi in the fanfic, there would be a lot of changes. First, his physical abilities would be off the charts. He could probably move at incredible speeds and have superhuman strength. His chakra reserves would be massive, which means he could perform powerful jutsu without getting tired easily. Also, the other characters in the story would probably be in awe or fear of him. His friends might try to help him control this new power, while his enemies would be even more determined to defeat him. It could also change the political situation in the ninja world, as having such a powerful being among them would disrupt the balance of power.
When writing, be creative with the power combinations. Let Naruto's Juubi - enhanced abilities interact in unique ways with the sacred gears or magic in Highschool DxD. For the story's atmosphere, blend the more serious and battle - oriented tone of Naruto with the sometimes comical and fan - service - heavy nature of Highschool DxD. And don't forget to give the story a proper ending, whether it's a happy ending where everyone becomes friends or a more bittersweet conclusion.
If Naruto absorbs the Juubi in fanfic, it could change the whole Naruto universe in that story. He may have new forms or abilities. Maybe he could use the Juubi's power to bring peace to the ninja world more quickly. He could also face new challenges as other characters might fear his new - found power.
In a fanfic scenario where Naruto becomes the Juubi, it's a game - changer. Firstly, his appearance would probably change significantly, maybe having some Juubi - like features. His speed, strength, and the range of his jutsu would increase exponentially. He could use the Juubi's power to heal the land that has been damaged by years of war. However, there would also be those who see him as a threat and try to stop him, believing that no one should possess such power. This would create a lot of conflict and drama in the fanfic.
There could be other characters too, like the Sage of Six Paths. He might play a crucial role in the Juubi's birth in the fanfic. And also, villains from the Naruto universe could be involved, as their actions might have either directly or indirectly led to the birth of the Juubi.
Well, perhaps in the fanfic, Naruto has to team up with his friends in a unique way to seal the Juubi. For example, Sasuke could use his Sharingan to help Naruto locate the weak points of the Juubi while Naruto does the actual sealing. And Sakura could use her medical ninjutsu to keep Naruto in top shape during the process.