If the OC has some kind of bloodline limit, the baby might inherit it. Along with Naruto's Uzumaki clan traits. Naruto has strong life force and chakra reserves, so the baby could have enhanced versions of those. It could also have the ability to sense danger like Naruto does, but in a more refined way. And who knows, it might develop a completely new power that's a blend of both Naruto and the OC's latent abilities.
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.
The baby could inherit Naruto's chakra reserves and his ability to use the Rasengan. Since Naruto has an enormous amount of chakra, it would make sense for the baby to also have a large chakra pool. The Rasengan is one of Naruto's signature moves, and it could be passed down genetically or through training that Naruto would give the baby as it grows up.
Another possibility is that the baby has a combined power. It could use water to create illusions, a mix of Percy's water control and Annabeth's strategic thinking. So when in a fight, it could create false images of itself using water to confuse the enemy and then attack from an unexpected angle.
In fanfiction, their baby could potentially have a unique power related to nature manipulation. Since Naruto has a connection with the Nine - Tails, which is a form of nature energy in a way, and Shion has her own spiritual powers. The baby might be able to combine these to create a new form of nature - based jutsu. It could also have the power of enhanced speed and strength, like Naruto, along with Shion's ability to sense danger on a spiritual level, which would give it an edge in combat and survival.
The baby might inherit Naruto's ability to use the Nine - Tails' chakra. Since Naruto has a strong connection with the Nine - Tails, it's possible for the baby to have some form of access to that power. This could manifest as enhanced strength and speed, similar to when Naruto taps into the Nine - Tails' chakra.
The baby could have the power of compulsion like Klaus, being able to influence the minds of others. Since Elena was a vampire too, the baby might also inherit enhanced strength and speed.
The baby could add a whole new dynamic to the plot. It might become a target for villains who want to use it against Naruto. For example, if the baby inherits Naruto's unique powers, enemies could try to kidnap it to study or control those powers. Also, Naruto would have to balance his duties as a hero and a father, which could lead to some interesting internal conflicts.
The baby might have some of Naruto's chakra - related powers. Since Naruto has the Nine - Tailed Fox's chakra, the baby could inherit a portion of that incredible power source. Also, Kurenai is skilled in genjutsu, so the baby could have a natural aptitude for that as well.
In fanfiction, if Naruto and Yoruichi had a baby, the baby could potentially have a wide range of powers. Naruto is known for his vast chakra reserves and his ability to use shadow clones and the Rasengan. Yoruichi, on the other hand, is a master of Shunpo and has cat - like abilities. The baby might inherit Naruto's chakra control and Yoruichi's speed, creating a unique combination. For example, it could use chakra - enhanced speed to quickly move around the battlefield and then deliver a powerful Rasengan - like attack with a touch of Shunpo - style finesse.
The baby could have Naruto's ability to use the Rasengan. Since Naruto has mastered this powerful technique, it might be passed down genetically or through training. Also, it could inherit Samui's intelligence and strategic thinking. This combination would make the baby a very formidable ninja.
Perhaps the baby's existence could be a catalyst for peace between Konoha and the Hidden Mist. The two villages, which had a history of conflict, could see the baby as a symbol of a new beginning. The story could revolve around Naruto and Haku trying to raise the baby while also navigating the political tensions between the two villages, and how they work towards a more unified ninja world.