In fanfiction, the Naruto Reverse Harem Jutsu used on Kaguya could lead to some really interesting scenarios. Maybe it could be used as a comical moment to catch Kaguya off - guard. For example, she might be in the middle of some grand, menacing plan when suddenly the jutsu is cast and she's surrounded by a bunch of Naruto clones all vying for her attention in a rather silly way. This could potentially disrupt her concentration and give the protagonists an advantage in the fight.
Maybe Sasuke. Although they are rivals, they also have a deep bond. Sasuke might have come across a unique jutsu during his travels and decide to teach it to Naruto so that they can both become stronger and better protect their village.
It could be a new form of Rasengan. Maybe Naruto discovers a way to combine different elements with the Rasengan more effectively, like adding lightning to it for a more powerful and faster attack.
Often, it can show a different side of Kaguya. She's so powerful and usually in control, but the jutsu can make her seem more vulnerable as she has to deal with this strange and unexpected situation. For example, she might have to waste time trying to figure out what's going on with these clones instead of focusing on her main goals.
Well, in certain fanfic scenarios, Naruto could learn paper jutsu as a result of some experimental training. For example, he might be trying to combine different elements of his existing jutsu and accidentally discovers a way to manipulate paper. It could be that his chakra takes on a new form during a particularly intense training session and he realizes he can control paper with it.
One interesting Naruto secret jutsu in fanfiction could be a time - traveling jutsu. It allows Naruto to go back in time and change certain events in the ninja world. This can lead to all kinds of new storylines and character developments.
If Naruto has a new secret jutsu in fanfic, like a super - powerful healing jutsu, it could change the story by allowing him to save more lives during battles. For example, he could heal injured comrades immediately and keep them in the fight. This would boost the morale of his side and potentially change the outcome of many battles.
There could be a jutsu that allows for instant teleportation across long distances. This jutsu might be a new discovery in the fanfiction world, perhaps created by a character who has been experimenting with space - time ninjutsu. They might use it to quickly get in and out of battles or reach far - off places in a blink.
Kaguya might start with chakra control training. Since she has such a deep understanding of chakra, she could teach Naruto how to refine his chakra even more. For example, she could show him how to make his chakra flow in a more stable and efficient way. She may also use her knowledge of space - time ninjutsu to train Naruto in that area. Maybe she'd create special training grounds using her space - time abilities to test Naruto's reaction and adaptability.
Kakashi can be a popular character too. His wisdom and combat skills can be useful in fanfic scenarios involving Kaguya. He could be a mentor figure to Naruto, guiding him in dealing with Kaguya - related threats or helping to decipher ancient ninja knowledge related to Kaguya.