One interesting combination could be Naruto's Rasengan with the power of the Pika Pika no Mi (Glint - Glint Fruit). He could create a Rasengan that emits intense light, blinding his opponents as he attacks. Another could be using his Shadow Clone Jutsu with the Mera Mera no Mi (Flame - Flame Fruit). His clones could all be on fire, creating a very intimidating and powerful offensive.
Well, Naruto would probably become more confident. With all those devil fruit powers, he could be even more fearless in battles. He might start to rely less on his original ninja skills and more on the unique abilities from the devil fruits, which could change his fighting style drastically.
Naruto's chakra could potentially disrupt the Devil Fruit powers. Since Naruto has a large amount of chakra, it might be able to interfere with the energy that the Devil Fruit gives Shiki. For example, if Shiki has a Devil Fruit that gives him the ability to create illusions, Naruto's strong chakra presence could break through those illusions.
The powers of devil fruits can be integrated by having characters discover them in a strange new land that has a connection to both the Naruto and One Piece universes. For example, a portal could open up and Naruto and his friends find a devil fruit tree. They then have to figure out how these new powers work within the context of their own ninja abilities. Maybe the devil fruit powers can be combined with chakra to create even more powerful attacks.
It can blend the powers by having characters use Devil Fruit abilities in the context of Naruto's combat system. For example, using Devil Fruit - based speed or strength enhancements during a taijutsu fight. The bloodline aspect could come in where certain families have an affinity for specific Devil Fruits, and they train to combine their bloodline - related chakra control with the fruit's power.
If Naruto ate a Paramecia Devil Fruit, his physical abilities might change drastically. For example, if it was a rubber - like Paramecia fruit, his already acrobatic fighting style could become even more so. He could stretch his limbs to attack from unexpected angles, much like Luffy in One Piece. This would give him an edge in close - combat situations, and his opponents would have a hard time predicting his moves.
If Naruto had the Fire Devil Fruit, his combat style would change drastically. He could combine his existing ninja skills with the power of the fruit. For example, he might be able to infuse his Rasengan with fire, making it even more powerful. Also, his mobility could be enhanced as he could use fire to propel himself in new ways. This would make him a more formidable opponent in battles against strong foes like Sasuke or Pain.
One interesting crossover could be Naruto having the power of the Gomu Gomu no Mi (Rubber - Rubber Fruit). He could use his ninja skills in combination with the stretching abilities. For example, he could stretch his arm to surprise - attack enemies from a distance while still being able to perform his signature Rasengan. Another could be a character like Sasuke with the power of the Yami Yami no Mi (Dark - Dark Fruit), which would enhance his already dark and brooding nature and give him new powers to control darkness and absorb attacks.
The most interesting aspect is the combination of powers. Naruto characters already have their own unique ninja abilities, and when you add devil fruits from One Piece, it creates a whole new range of power combinations. For example, a character with a Logia - type devil fruit could become nearly invincible in Naruto's world, which would completely change the dynamics of battles.
A Devil Fruit that allows the male OC to control gravity would be really cool. He could make himself or others extremely heavy or light, which would be useful in battles and for traversing difficult terrains like mountains or quicksand areas in the One Piece world.
One consequence could be that the character becomes a target. Since having the ability to copy Devil Fruit powers is extremely powerful, many villains would want to either control or eliminate the character. This would put the character in constant danger.