Naruto could be doing it for the sake of inspiring others. He doesn't want young ninja trainees to see his scars and be afraid of getting hurt in battles. By hiding his scars with genjutsu, he presents himself as a perfect, unblemished hero, someone that the young ones can look up to and strive to be like without the fear of being permanently marked by their battles.
Perhaps Naruto is tired of the pitying looks he gets from people when they see his scars. By hiding them with genjutsu, he can avoid those uncomfortable moments and be treated as just Naruto, the powerful ninja, rather than Naruto, the one with the scars. Also, he may not want his enemies to see his scars and think they've managed to truly harm him, so he uses genjutsu to keep up a facade of being unscathed.
In the fanfiction, Naruto might use his chakra control skills to create a genjutsu that alters the perception of those who see him. He could project an image of his unscarred self over his actual body. For example, he focuses his chakra on the area around his scars and manipulates the light and the way it reflects off his skin in the eyes of others, making the scars seem to disappear.
One possible reason could be that he doesn't want others to pity him. Naruto has always been a proud and strong - willed character. His scars might be a reminder of painful past experiences, and he prefers to deal with them privately rather than showing vulnerability to others.
In the context of fanfiction, it might also be a plot device to explore Naruto's vulnerability. It could lead to new character developments, such as others seeing him in a new light. Maybe it causes some characters to re - evaluate their relationship with him, while for others it could be a source of inspiration, seeing that even someone as strong as Naruto has his own set of hardships.
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.
He might show his scars to Sasuke. Given their complex relationship, it could be a powerful moment between them, a way to show Sasuke that Naruto has also faced great pain in their separation and the events that followed.
One possible motivation could be his deep - seated longing for his parents. Naruto has always felt their absence and has craved their love and approval. Jumping in front of them could be his way of showing that he is worthy of being their son and that he can protect them, even if it's in a situation that defies the normal order of things. It's like he's trying to rewrite the past in a way, to be the hero for his parents that he has become for the village.
He could use a simple disguise like a cloak with a hood. This is a classic way to hide one's face and body shape. Just like in many stories, a large, dark cloak can make it hard for people to see who is underneath. He could also keep the hood up to shadow his face.
Naruto's scars might be a sign of his loyalty and self - sacrifice. He has always been willing to put himself in harm's way for his friends and the village. The rookie 9 seeing these scars could make them realize how much Naruto has done for them. For instance, his scars from fighting Pain were to protect the village and his comrades. It's a physical manifestation of his unwavering spirit.
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.
One possible reason could be that he is on a secret mission and doesn't want to be recognized. He might be infiltrating an enemy organization or spying on someone. Another reason could be that he has some new power or mark on his face that he wants to keep hidden until he fully understands or masters it.