First, give the OC a unique backstory. Maybe they got the Absorption Devil Fruit by accident, like finding it in a hidden chest on an abandoned island. For their appearance, you could give them markings on their body that glow when they use their power. In terms of personality, make them curious. Since they can absorb different things, they would always be eager to test the limits of their power. For example, they might be the type to immediately try to absorb a strange new substance they come across.
An example of a novel where the protagonist possessed the power of the Devil's Fruit was as follows:
1 One Piece: As the protagonist of One Piece, Luffy gained the power of the Devil's Fruit as he grew up and became a powerful pirate. He constantly challenged powerful enemies and gradually grew into a leader in the process.
2 Naruto: As the protagonist of Naruto, Naruto Uzumaki also has the power of the Devil's Fruit. His rubber fruit allowed him to control his body freely, making him a very powerful ninja.
[3]<< Death >>: The sword is an important element in Death. After the main character, Aizen, disposes, he obtains the power of the Devil's Fruit and becomes a Devil's Fruit user who can use the " Magic Wand ".
4. Inuyasha: The protagonist Inuyasha also obtained the power of the demon fruit during his growth. His Inuyasha Soul Fruit allowed him to use all kinds of weapons and magic to become a powerful warrior.
5 " Sword God Realm ": The protagonist, Kirito, was a gaming enthusiast. He obtained the power of the Devil's Fruit in the game world and became a ninja who could control the game world.
The Demon Fruit was a magical fruit that could grant the consumer superhuman strength and speed. In One Piece, the protagonist Luffy obtained the power of the Devil's Fruit during an adventure and became a powerful pirate.
Luffy's Devil Fruit ability allowed him to transform into a rubber man with super elasticity and shapeshifting abilities. He could also release powerful rubber gas to make his body incomparably strong.
In the story of One Piece, Luffy and his pirate team experienced many adventures, including decisive battles with other pirates and naval battles, as well as exploring the mysterious world map. Luffy and his team continued to grow and overcome many difficulties together, eventually becoming a great pirate leader.
Another possibility is a Devil Fruit that gives her the power of telepathy. Fem Luffy could then communicate with her crew without speaking, which would be very useful in stealth missions. She could also use it to read the minds of her enemies, getting an edge in battles. This would completely change the dynamics of her relationships with other characters in the story as well.
One idea could be that Naruto somehow obtains a Dragon Devil Fruit. He then gains the abilities like flying, breathing fire or some other dragon - like powers. This would completely change the dynamics of his battles in the Naruto universe. He could use his newfound flight to gain a strategic advantage over his opponents and his fire - breathing could be a powerful offensive move.
The reaction would be mixed. The Hidden Leaf Village might initially be excited as Naruto is always finding new ways to protect them. But as they realize the implications of a Devil Fruit power, there could be concerns. Other villages would likely be intimidated. They might start to form alliances against the Leaf out of fear that Naruto's new power could be used to dominate them. However, some shinobi might also be inspired by Naruto's new ability and try to find ways to counter it, which could lead to a new era of power - seeking and innovation in the ninja world.
Another interesting concept is to cross the devil fruits with the world of Harry Potter. Imagine a character with a devil fruit ability like the ability to turn into an animal (zoan type) trying to blend in at Hogwarts. They might have to hide their powers from the wizards while also using them to their advantage in the magical world, like using their animal form to explore hidden areas of the school.
One idea could be a story where Naruto somehow gets a devil fruit that gives him the power to control water. He could use it in his battles in the Naruto world, like creating huge water jutsus with the unique properties of the devil fruit power. Another idea is to have a crossover where characters from One Piece come to the Naruto world and Naruto has to deal with the chaos that the devil fruits bring along.
One idea could be that the OC uses the Magma Devil Fruit to create new forms of terrains. For example, they could form volcanic islands in the middle of the ocean, which would change the geography and power dynamics in the story's world. They might also use the magma to create defensive barriers that are almost impossible to penetrate, like a ring of molten rock around a city they are protecting.
One interesting idea could be that Luffy has to rely solely on his Haki and physical training, making him even more of a badass in combat. He might develop unique fighting styles that we haven't seen in the original story where he had devil fruit powers.