There are some great ones. Some authors combine the unique abilities of the Gum Gum Fruit from One Piece into the Naruto universe in really creative ways. For example, they might have a character with the powers of the Gum Gum Fruit training at the Ninja Academy, which leads to all sorts of interesting scenarios and interactions with the original Naruto characters. You can also check out some of the reviews on the fanfiction platforms to find the most popular and well - written ones.
Common themes include the idea of an outsider. Since the Gum Gum Fruit is from a different universe, a character with its power can be seen as an outsider in the Naruto world. This can lead to themes of acceptance or discrimination. Also, adventure is a big theme. Using the Gum Gum Fruit powers to go on quests or explore new areas in the Naruto universe is quite popular in these fanfictions.
In fanfiction, if Naruto ate the Gum - Gum Fruit, he would likely gain some really interesting abilities. He could stretch his limbs like Luffy from One Piece. This would give him a whole new fighting style. He might be able to stretch his Rasengan - holding hand to surprise his enemies from a long distance. Also, his acrobatic skills would be enhanced as he could use his stretched body parts to swing around like a slingshot.
I recommend the book "Possibly a Fake Silver Soul". It tells the story of Jiang Cheng, a transmigrator, who met the owner of Xinghai District and his girlfriend, Jiang Hua, who were traveling in the universe in the dragon vein of a certain planet. Later, he came to Earth and met his teacher, Yoshida Shoyo, who had influenced his life. He also met a group of friends. This included the transmigrator Okita Soki. This is a Silver Soul Doujinshi novel, don't miss it. I hope you like this fairy's recommendation. Muah ~😗
Another concept might be the creation of new spells or magical items inspired by the Gum Gum Fruit. Maybe a spell that gives an object the ability to stretch like the Gum Gum Fruit. This could be used in various situations, such as in a duel or to reach something in a dangerous place.
Gintama is purely fictional. It's filled with imaginative characters and scenarios that are not rooted in real-life events. The creators crafted a unique and entertaining fictional world for the audience.