In most One Piece canon, a person can't eat multiple devil fruits due to the risk of exploding. However, in fanfiction, the rules can be bent. Some fanfictions might allow Luffy to eat multiple devil fruits by creating special circumstances or new powers that counteract the normal limitations. For example, a fanfiction could introduce a powerful magic or a unique ability that enables Luffy to safely consume and control the powers of more than one devil fruit.
If Luffy ate multiple devil fruits in fanfiction, it would likely make him extremely powerful. His existing Gum - Gum powers are already quite strong, but adding more devil fruit powers would be insane. He could have abilities like teleportation from one devil fruit and the ability to turn invisible from another. This would completely change the power dynamics in the story. Enemies that were once a challenge would become much easier to defeat. However, it could also bring new challenges. Maybe the new powers are difficult to control at first, and Luffy has to struggle to master them. Or perhaps there are side - effects to having multiple devil fruits that he has to deal with.
Another idea is a Devil Fruit that gives Luffy the ability to transform into different animals. He could turn into a powerful eagle to fly over islands and scout for danger or transform into a strong bear to have enhanced strength and endurance in close - combat battles. This would change his fighting style completely and make for some really interesting interactions with his crew and opponents.
He could eat the Pika Pika no Mi (Glint - Glint Fruit) which gives the power of light, allowing him to move at the speed of light and create powerful light - based attacks. And perhaps the Yami Yami no Mi (Darkness - Darkness Fruit) which can absorb other attacks and create a gravitational pull. Combining the powers of light and darkness would be quite a unique and powerful combination for Naruto in this fanfiction.
One potential combination could be if Naruto ate the Ope - Ope Fruit (giving surgical - like powers) and the Inu - Inu Fruit (Dog). He could use the Ope - Ope powers to manipulate his body parts while in his Dog form, perhaps making his attacks more precise or his defenses stronger. This would also open up a whole new set of strategies for him in battles. It's all about how the fanfiction author would choose to blend these very different power sets and how Naruto would learn to use them effectively.
There were many different demonic fruits in One Piece, and the following were ten of them:
1. Demon Fruit-After eating it, you will gain the ability to change yourself or others 'abilities such as flying, transformation, elemental manipulation, etc.
2. Rubber-like fruit--can create rubber-like elasticity that allows one's body to bounce, transform, bend, etc.
3. Demon Fruit--After eating it, you will gain the ability to control flames, such as using fireballs or flame jets to attack enemies.
4. Demon Fruit--After eating it, you can control water, such as using a water gun or a water column to attack enemies.
5. Demon Fruit--After eating it, you will gain the ability to control the wind, such as using a wind sword or wind blade to attack enemies.
6. Demon Fruit--After eating it, you will gain the ability to control lava, such as using lava waves or lava jets to attack enemies.
7. Demon Fruit--After eating it, you will gain the ability to control earthquakes, such as using earthquake waves or earthquake attacks to attack enemies.
8. Demon Fruit--After eating it, you will gain the ability to control lightning, such as using lightning waves or lightning attacks to attack enemies.
9. Demon Fruit--After eating it, you can gain the ability to control ice, such as using ice swords or icicles to attack enemies.
10 Demon Fruit-After eating it, you will gain the ability to control black holes, such as using black hole waves or black hole attacks to attack enemies.
One Piece's Devil Fruit was an ability that granted the consumer a special ability. Currently, One Piece's top ten demonic fruits were:
[1. Devil Fruit-Fire Ball: Able to allow the user to shoot fireballs at the enemy.]
[2. Demon Fruit-Iceberg: Able to turn the user into ice and freeze the enemy.]
[3. Devil Fruit·Magma (Magma): Able to turn the consumer into magma and melt the enemy.]
4. Devil Fruit-Lightning: Able to allow the user to shoot lightning at the enemy.
[5. Devil's Fruit-Gravity: Grants the user the ability to fly or fall freely in the air.]
[6. Demonic Fruit-Wormhole (Wormhole): Able to allow the consumer to quickly move to other places through a wormhole.]
[7. Demon Fruit, Fruit Ability (Fruit Awakening): Able to allow the consumer to obtain the ability of other demon fruits, such as the ability of rubber fruit, swelling and jumping.]
[8. Devil's Fruit, Nage Mode: Grants the user defensive and offensive abilities to enhance their combat ability.]
[9. Demon Fruit, transparent fruit (transparent fruit): Able to make the consumer invisible or able to pass through walls.]
10 Demon Fruit, Demon Strayer: Grants the user the ability to quickly traverse through Demon Island and other regions.
In the Naruto universe, Devil Fruits are from One Piece, and Naruto's world has its own power system like chakra. So, it's highly unlikely in the original Naruto story. However, in fanfiction, anything can happen. The author might create some kind of crossover logic to make it possible, like a strange portal connecting the two universes.
Well, he might gain new powers which could make him more confident. For example, if one of the devil fruits gives him the power of flight, he would feel more powerful and it could change his approach to battles. He might become a bit more adventurous too, as he explores the limits of his new abilities.
If Luffy ate a different devil fruit, his entire power set and character would change drastically. For example, if he ate a Logia type like the Smoke - Smoke Fruit, his fighting style would be more about evasion and stealth. He could turn into smoke to avoid attacks, and his stretching abilities would be gone. His crew might also have to adjust their battle strategies around his new powers.