In this fanfiction scenario, Naruto could potentially use new and untested jutsu. He might draw on the power of his nine - tailed fox in a completely different way. Maybe he'd combine Sage Mode with some secret Uzumaki clan technique he discovers during the fight.
In a 'naruto fights alone fanfiction', it could be that Naruto is on a mission in a foreign land where he has no support. The local ninjas are all against him for some reason. He has to use his Nine - Tails chakra in a more discreet way as he can't afford to go all - out and draw too much attention. He might befriend some local animals or spirits who help him in a more indirect way, like giving him information about the enemies' weaknesses.
One possibility is that Naruto's chakra nature could change completely. Since Kaguya had unique chakra, Naruto might develop new jutsu that are a blend of his own and Kaguya's abilities. For example, his Rasengan could gain the power to not only attack but also to heal, as Kaguya had some form of life - giving power. Also, his connection to the tailed beasts could be enhanced in unexpected ways, allowing for better communication and cooperation with them.
In such a fanfiction, Naruto could potentially win by using his new Sage of Six Paths powers to their fullest. He might be able to overpower Madara's Rinnegan abilities. For example, Naruto could use his massive chakra reserves to create countless shadow clones and overwhelm Madara in a battle of attrition.
Well, Naruto might use his unique jutsu like Rasengan in new and creative ways against the combined forces of the 5 nations. Maybe he would form new alliances within the 5 nations to fight against a common hidden enemy that threatens them all.
Maybe an ancient evil ninja who was sealed away long ago but has now been released. This antagonist could have powers that nullify any communication or summoning jutsu, forcing Naruto to fight alone. He would be extremely powerful and know many forgotten and deadly jutsu.
In this fanfiction, Naruto would likely have a huge power boost. Since Kaguya has such vast knowledge and power, she could train Naruto to better control his already massive chakra reserves. Maybe she'd show him how to use chakra in ways he never thought of before. For example, she could teach him to infuse his rasengan with some of her own unique chakra elements, creating a new and super - powerful attack. Also, Naruto's understanding of the origin of ninjas and the world itself could deepen through Kaguya's teachings.
Well, in such a fanfic, Percy would probably have to dig deep into his own skills and experiences. Since he's alone, he can't count on Annabeth's strategic thinking or Grover's sensing abilities. He might have to face a god who's out to get him. He'd be forced to use his powers in creative ways, like using his water - control to escape from a labyrinth - like trap instead of having someone else to help him find an exit.
The fanfiction could start with Harry being magically transported to Kaguya's world. He'd be confused at first but quickly realize he has to fight to survive. Harry's wand would be his main weapon. He might learn some new spells during the fight, perhaps a spell that can nullify Kaguya's ability to freeze time. As the fight progresses, both characters would start to respect each other's power, leading to an unexpected alliance at the end.
In this fanfiction, Naruto could be visited by the spirit of his father, Minato. Minato could offer some words of wisdom and comfort to Naruto on his birthday. They might have a heart - to - heart conversation about Naruto's growth as a ninja and his future in the village.
Well, Naruto might first try to free Kaguya. He is a hero after all and doesn't like to see anyone chained unjustly. But he would also be very cautious because Kaguya is extremely powerful and was once a great threat. He could try to communicate with her to understand why she is chained there in the first place.