In some cases, it's just a creative way to make the characters more visually distinct and memorable. It can also be a plot device to hint at hidden identities or mysterious backgrounds.
The novel often showed the changes in the character's heart and emotions through the details of the character's eyes, movements, language, and so on. For example, a character initially had a firm attitude towards something, but as the plot developed, his or her eyes, tone, and other details changed, implying that the character's inner thoughts had changed.
Fictions could also be used to describe the relationship between characters to show a change in expression. For example, a character who had been prejudiced against another character before, but as the plot developed, he or she gradually discovered the advantages of another character and began to change his or her opinion. This kind of description could let the readers feel the changes between the characters and the changes in emotions.
The novel could also use the plot twist to reflect the change in the eyes. For example, a character originally intended to do something, but as the plot developed, he or she changed his or her mind and gave up on the original plan. This kind of plot twist allowed the reader to feel the changes in the character's heart and emotions.
In short, the novel could use various ways to show that the readers could feel the changes between the characters and the changes in emotions when they made eye contact.
The story would become much more intense. Naruto would suddenly have access to powers that were previously exclusive to the Uchiha. This would shift the power balance in the ninja world.
I recommend the Treasure-Seeking Divine Eyes to you. The male protagonist, Li Mo, obtained an eye that could change at will in an accident. He could see all kinds of precious treasures and changed his entire life. Although he couldn't control the color of his eyes, this novel reminded me of the plot you mentioned. I hope you like my recommendation. Muah ~
Yes, there might be. The Naruto and Attack on Titan fandoms are both huge, and fans often like to cross over their favorite characters in fanfiction. So it's quite possible to find Eren - from Attack on Titan - in Naruto fanfiction. However, it may not be as common as fanfictions within each respective universe.
The Snake Eyes origin story could have changed to fit in with new plot developments or to introduce fresh elements to the character. Maybe it was to keep up with evolving audience expectations or to differentiate from previous interpretations.
I really don't know. Maybe it's a complex storyline or a sequence of events that takes up 11 hours of the narrative. Without having read the novel, it's difficult to give a definite answer.
Well, it could make his combat style more versatile. He might be able to analyze his opponents' moves more precisely. With six eyes, he could have a wider field of vision, detecting attacks from more angles. Maybe he can use this new visual ability to anticipate his enemies' actions better and counter them with more effective jutsu combinations.