Another possibility is that it could be a part of a self - discovery arc in the fanfiction. Maybe Naruto starts to question his own identity and through various interactions and experiences, he decides to reveal his true gender as a way to be more true to himself.
Sasuke, on the other hand, might act like he doesn't care much on the surface, but deep down he would be a bit confused and might start to see Naruto in a new light. He's not very good at expressing emotions, so his reaction would be more subdued.
Kakashi could be involved too. Given that Kakashi has trained Naruto and seen his growth, Naruto might trust him with his secrets. He could reveal his thoughts on how he wants to change the ninja world for the better and the steps he is planning to take in the future.
Another possibility is that he reveals secrets about his parents. He could talk about things his father, Minato, told him in a dream or some information he discovered about his mother, Kushina, that no one else knows. For example, a secret mission they were involved in or a special bond they had with certain characters in the Hidden Leaf Village.
One possible significance could be a sign of his growth and the battles he has endured. His scars are like a visual record of his journey, showing how he has overcome difficulties. They might also be a way to connect with other characters on a deeper level, as they can see the physical toll his life has taken.
They would probably be shocked. Since Naruto is such an important figure to them, any big secret would likely cause a stir. For example, if it's about his Nine - Tails secret, they might be initially stunned as they realize how much he has been carrying alone.
It's possible he gains enhanced physical abilities like super strength or speed. Since his heritage is often tied to some special genetic traits, these could be unlocked upon the revelation. For example, if his heritage is linked to a powerful clan, he could inherit their natural combat prowess. He could also find out about special chakra control abilities that are exclusive to his bloodline, which would give him an edge in battles.
Some characters might be shocked and saddened. They may have known Naruto as a strong and energetic person, and seeing his scars would make them realize the hardships he has faced.
Well, it could strengthen his bonds. His friends might see him in a new light, with more understanding and respect. For example, they could realize the weight of his past and be more empathetic towards his struggles.
One reason could be some sort of experiment. Maybe Orochimaru or another villain was trying to create a super - ninja and combined the genetic material of the Uchiha with Naruto's. Another possibility is that it's a gift from a powerful being. For example, a god - like entity could have bestowed the Sharingan on Naruto to help him in his quest to bring peace to the ninja world.