One key moment could be when Naruto is in a life - or - death battle and has no other option but to dig deeper into Kurama's chakra. That's when he starts to get a real feel for it.
Once Naruto masters Kurama's chakra in the fanfiction, his fighting style is revolutionized. He is no longer just relying on his regular ninja skills. The Kurama chakra infusion allows him to enter a more powerful state. He can now use the chakra to boost his jumps, making him able to cover large distances in a single leap. His attacks also carry a new level of ferocity. He can channel the Kurama chakra into his weapons, if he uses any, to make them more effective. Moreover, he can use the chakra to create a sort of protective aura around him, which can deflect or absorb some weaker attacks. This all - around improvement in his fighting capabilities makes him a formidable force in the fanfiction world.
Naruto himself would probably be one of the main ones. He's always been associated with powerful chakra use in the original series, and in this fanfiction, with only males using chakra, he would stand out even more. Another could be Sasuke. His chakra abilities are also quite remarkable, and he would be a key male character in terms of chakra use in this fanfiction.
In some fanfictions, Naruto might use chakra strings in a similar way to how Sasuke uses his chakra to control his sword. He could send out his chakra in the form of strings to manipulate objects from a distance. For example, he could use them to pull weapons out of an enemy's hand or to tie up an opponent.
He might rely on his physical strength and martial arts skills. Naruto is known for his tenacity and determination. Without chakra, he could train his body to be extremely strong, like a super - athlete. He could use his speed and agility to dodge attacks and land powerful punches and kicks.
Well, it could limit the power dynamics in the story. Since only males can use chakra, female characters might have to rely on other skills or abilities. This could lead to a more distinct separation between male and female roles, with males being the main fighters due to their chakra use.
His friends might respect his decision more. They know how powerful the Kyuubi's chakra is, but also understand Naruto's reasons for not wanting to use it. This could strengthen their bond as they see Naruto's integrity.
In some fanfictions, Naruto might learn to use chakra chains through special training. Maybe he discovers a new form of chakra control or he is taught by a mysterious character who has knowledge of this unique ability.
If Naruto couldn't use chakra, the entire story would be drastically different. Firstly, he wouldn't be able to perform his signature jutsus like the Rasengan. His training with Jiraiya would also take a different turn as they couldn't focus on chakra - based skills. Without chakra, Naruto might have to rely more on his physical strength and strategic thinking. He could develop unique fighting styles that don't involve chakra, perhaps something similar to real - world martial arts. This would also change his relationships. For example, Sasuke, who is very chakra - powerful, might view Naruto in a different light. It could lead to a more complex and less predictable plotline.
Sasuke Uchiha could be one. Since he has the Rinnegan in the later parts of the Naruto series, it's possible that in fanfiction he could be using chakra chains in connection with his Rinnegan powers. Another could be Naruto Uzumaki if the fanfiction has some kind of plot twist where he also gains access to the Rinnegan and uses chakra chains in a new and unique way.