He could have enhanced vision powers, like seeing through illusions more easily or being able to detect chakra signatures from a much greater distance. The red eye might act as a sort of sensor, similar to how the Byakugan can detect things, but with its own unique properties.
It's possible that the red eye allows him to tap into a different type of chakra, like a darker or more primal form of chakra. This new chakra source could give him access to new jutsu that are more powerful and unpredictable compared to his normal abilities. For example, he might be able to create black flames or use a form of lightning jutsu that has a red tint to it.
The third eye might have the power of long - distance vision. Naruto could use it to spy on enemy camps or look for missing comrades from afar. This would be a useful addition to his skills, especially when planning strategies or rescuing hostages. He could also use it to keep an eye on the Akatsuki's movements across different regions without having to be physically close.
Perhaps it's a dojutsu that can manipulate the elements in a new way. For instance, it could turn his wind - style jutsu into something more powerful and less predictable. It might also have the ability to absorb the chakra of his opponents when he makes eye contact with them, which would give him an edge in battle. The appearance of the dojutsu could be something like a swirling pattern in his eye.
Naruto might embark on a journey to find out the origin of the Millennium Eye. This could lead him to different hidden villages or ancient ruins. Along the way, he'd face various challenges and enemies who are also interested in the power of the Millennium Eye. He may have to use his new - found power to overcome these obstacles and protect his friends.
In fanfiction, Naruto as a celestial wizard could possess the power of celestial star magic. This type of magic could allow him to use the power of the stars for various purposes. He could create powerful star - based attacks, like shooting star beams at his enemies. He could also use the stars to navigate through different dimensions or gain knowledge about future events, adding a whole new layer of mystery and power to his character.
Maybe Naruto would have the power of cosmic energy projection. He could shoot out powerful blasts of energy that are a mix of his chakra and cosmic forces. This would be a great offensive weapon against the Avengers' enemies.
It could have the ability to see chakra flow in extreme detail. This would allow Naruto to detect hidden traps or enemies who are using chakra - concealment techniques. He could also use it to analyze the weaknesses in an opponent's jutsu just by looking at the chakra patterns.
The baby could potentially have Naruto's chakra powers. Since Naruto has a vast amount of chakra and can access the Nine - Tails' power, the baby might inherit some of that. Maybe it could also have some unique abilities from the OC. For example, if the OC has a special type of jutsu related to nature manipulation, the baby could have a combined form of that and Naruto's powers.
It might be due to some sort of bloodline fusion. Naruto is known for his Uzumaki heritage, but perhaps there was an unexpected encounter with another clan's power that merged with his own, and as a result, one of his eyes turned red as a new and unique ability emerged.
A vampire in a Naruto fanfic might possess the power of hypnotism. This could be used to manipulate other characters, much like the Sharingan in some ways. They could also have the ability to transform into a bat - like form for quick movement or stealth. Additionally, they could have a regenerative ability that is much faster than normal Naruto characters, which is related to their vampiric nature.
Alucard might have the power of shapeshifting, which could be used to deceive his enemies in the Naruto universe. He could also have the ability to control shadows, a power that would be quite unique in the world of ninja. This would allow him to move stealthily and ambush his foes. Additionally, his immortality would be a huge advantage, as he could keep coming back in battles no matter how severe the damage.