In some fanfictions, Naruto having Kyuubi's eyes could signify a deeper connection to the Kyuubi's power. It might mean he can access its chakra more directly or even gain some of the Kyuubi's abilities related to perception, like seeing chakra more clearly.
One interesting concept could be the Kyuubi eyes having unique powers like seeing through illusions that even the Sharingan can't detect. This would give Naruto an edge in battles against powerful foes who rely on deceptive jutsu.
Often, in fanfiction, Naruto with Kyuubi's eyes is shown to have enhanced abilities. Writers may show him using the Kyuubi's eyes to see through illusions more easily. They might also describe his vision as being able to detect the slightest movements or changes in chakra flow. His appearance could also change slightly, with the eyes being a central focus. Maybe his pupils become slitted like a fox's, which adds to his overall otherness. This new look could also attract different reactions from characters in the story, from admiration to fear.
Yes, in some fanfictions, Naruto is often depicted as the Kyuubi or having a very close connection to it. This can lead to really interesting and unique storylines that deviate from the original plot.
Some fanfictions might depict the Kyuubi eyes as having a mind of their own. They could be constantly communicating with Naruto in a silent way, guiding his actions or warning him of danger. It's like they are a separate entity within him that he has to learn to work with.
One common plotline is the Kyuubi teaching Naruto new and powerful jutsu. Since the Kyuubi has a vast amount of chakra and knowledge, it could share unique techniques with Naruto that are not part of the regular ninja training. Another plotline could be the Kyuubi's influence on Naruto's relationships. For example, some fanfictions explore how Naruto's connection with the Kyuubi affects how his friends and villagers perceive him. It can also lead to some interesting character development as Naruto has to learn to control the Kyuubi's power without being consumed by it.
The ability could also affect Naruto's power on an emotional level. Knowing that Kyuubi can see through his eyes might make Naruto feel more confident. He might be more willing to take risks in battles or in exploring new areas. This new - found confidence could translate into him using his existing powers more effectively, like his Rasengan or his ability to summon toads. Also, Kyuubi might be able to spot things that can help Naruto improve his jutsu. For example, if there are certain natural elements or energy sources that Naruto can use to power up his jutsu, Kyuubi could see them through Naruto's eyes and tell Naruto how to utilize them.
In many Naruto fanfictions, Naruto might have developed some new and unique abilities that the Kyuubi has no defense against. This could make the Kyuubi, which is used to being a dominant and feared force, feel vulnerable. For example, if Naruto has the power to nullify the Kyuubi's chakra or to manipulate it in a way that goes against the Kyuubi's will, it would be a cause for fear.
They might have adventures where Kyuubi can use Naruto's eyes to sense hidden threats. For example, in a battle against an unknown enemy, Kyuubi could spot the enemy's hidden traps or ambushes through Naruto's enhanced vision. This would give Naruto an edge in combat as he could be alerted to the danger before it's too late.
Maybe it's because Naruto has some sort of special connection or resemblance to the Kyuubi that Kushina notices. For example, Naruto might display some of the Kyuubi's power characteristics in an obvious way that makes Kushina jump to that conclusion.