Well, it could be something like a fire - based kekkei genkai that allows Naruto to control blue - flame fire which is hotter than normal fire. This would give him an edge in battles and also a new look to his fighting style.
It could be a water - based kekkei genkai. Since the Wave arc has a lot to do with water, it would make sense for Naruto to awaken a kekkei genkai related to water. This could give him an edge in battles, especially in the Wave region where water is abundant.
One common combination is the Sharingan and the Rasengan. The Sharingan's ability to analyze and predict movements can be really useful when Naruto is forming and launching a Rasengan. Another could be the Byakugan and Sage Mode. With the Byakugan's enhanced vision, he can better sense the chakra flow around him in Sage Mode, making his attacks more precise. Also, sometimes you see him with the Ice Release along with his regular Wind Release. He could then create ice - infused wind attacks that are both cold and sharp.
Having a kekkei genkai in fanfiction could completely transform Naruto's journey. It might unlock hidden potential within him, affect his relationships with other characters, and introduce new conflicts and resolutions that weren't present in the original storyline.
Another possibility in fanfics is that Naruto could have a Kekkei Genkai that is related to space - time manipulation. This could be inspired by his connection to the Nine - Tails and the fact that he has access to a lot of chakra. With this Kekkei Genkai, he could teleport short distances or even create small pocket dimensions to store items or trap enemies.
In some fanfictions, a side character from the original Naruto series could be made into the main character. For example, Rock Lee. He doesn't have any Kekkei Genkai in the original, but in this fanfiction, he could be given one of the 9 Kekkei Genkai and the story could be about how he overcomes the limitations he had before with his newfound power.
One interesting kekkei genkai in Naruto fanfiction could be the ability to control time on a small scale. This would allow a character to freeze an opponent briefly in battle or speed up their own movements. Another could be the power to manipulate elements in unique ways, like combining fire and water to create a scalding steam attack. And there's also the kekkei genkai of telepathy, which enables a character to read minds and communicate mentally with others, giving them an edge in both combat and strategic planning.
In Akatsuki fanfiction, Sakura Haruno might be given a unique Kekkei Genkai. It could be something related to enhanced strength or perhaps a special type of medical ninjutsu on a whole new level. For example, her Kekkei Genkai could allow her to heal not just physical wounds but also mental traumas instantaneously, which would be a very interesting addition to her character in the context of Akatsuki fanfiction.
To integrate the Uzumaki clan's kekkei genkai into a new story line, consider creating a mystery around it. The main character could start off not knowing they have this kekkei genkai, but they keep experiencing strange events. As they investigate, they find out about their Uzumaki heritage and the kekkei genkai. They then have to figure out how to use it to solve the mystery of an ancient evil that is related to their clan. You can also have the kekkei genkai be a key factor in a tournament or competition. The Uzumaki character has to use their kekkei genkai in creative ways to win and prove the worth of their clan.
One interesting concept could be exploring an unknown kekkei genkai of the Uzumaki clan that gives them the ability to manipulate time on a small scale. For example, they could slow down time for a brief moment in battle, giving them an edge. Another idea is a kekkei genkai that allows them to communicate with the spirits of their ancestors, gaining wisdom and power from them. Maybe a kekkei genkai that lets them transform into a powerful beast form related to their clan symbol.