In fanfiction, if Luffy ate the Flame - Flame Fruit, he would gain the power of fire. His attacks could be infused with flames, making his Gum - Gum Pistol even more powerful. He could also use fire to defend himself, like creating a wall of flames around himself.
One possible plot could be that Naruto, with the power of the Flame - Flame Fruit, becomes even more powerful in combat. He could use the fire - based abilities of the fruit to enhance his existing jutsu, like adding a flaming element to his Rasengan. This would make him a more formidable opponent against enemies, especially those with water - based techniques.
One idea could be that Naruto somehow gains the power of the Flame - Flame Fruit. He could use it to create new and powerful jutsu, like combining the fire nature of the fruit with his own chakra to make a super - heated Rasengan. Another plot could involve Naruto using the fruit's power to protect Konoha from a new and powerful enemy that is immune to normal ninja attacks but vulnerable to the unique flames of the fruit.
His relationship with his friends might change. They would see him as even more of a powerhouse. Some might be in awe of his new power, while others, like Sasuke, might feel a bit of rivalry. Naruto would also have to learn to control the power of the fruit, which could be a struggle at first. This journey of self - control would make him more mature and responsible. He'd understand the importance of not misusing such a powerful ability and would strive to use it for the good of Konoha and his friends.
Luffy's character would develop in several ways. With the Flame - Flame Fruit, he'd have to learn to control the fire element. This would require discipline, which is something he doesn't have much of in the beginning. As he masters the power, he'd grow more responsible. Also, his reputation among other pirates and in the world would change. He'd be seen as an even more dangerous and unpredictable foe, which would add to his allure as a pirate captain.
In this fanfiction, Naruto's relationships would experience significant shifts. With his friends, they would initially be curious and a bit envious of his new power. However, as time goes on, they would learn to work with it. His relationship with the village elders might change too. They would likely be more cautious about Naruto, fearing the potential destruction that could come with his new, powerful ability. But Naruto, being Naruto, would strive to prove that he can use the Flame - Flame Fruit's power for the good of the village and its people, thus gradually earning their trust back and strengthening his bonds with them in the process.
Luffy, of course. He and Sabo have a deep history. They grew up together and Sabo was like a brother to him. Their reunion would be filled with joy, hugs, and probably a lot of tears. Luffy would be over the moon to have Sabo back in his life and on his ship.
There were many ways to use fruits to make the fruit peel. According to the descriptions of documents [2] and [4], you can choose different types of fruits, such as hawthorn, apples, carrots, etc. First, the fruit was cut into small pieces and then processed according to different methods. One method was to put the fruit into a steamer and steam it for a while, then put the steamed fruit into a food processor, add lemon juice, stir it into a fine fruit paste, and then pour it into a baking tray to bake. The other method was to put the fruit into the blenders and beat it into a fruit puree. Then, pour the fruit puree into the pot and cook it. Add lemon juice and continue to stir and cook. Finally, spread the cooked fruit puree on a flat plate or plastic wrap to dry and cut it into sections. The document [8] also mentioned a method of making the fruit peel. After the hawthorn was cooked, it was beaten into a fruit paste, then white sugar was added and stirred until it was thick. Finally, the jam was poured into a flat plate or a baking tray to dry. To sum up, one could choose a suitable method to make the fruit peel according to their personal preferences and the fruits they had.