Well, it might be a story where Knuckles' skills as a fighter are put to the test in the Naruto world. He could be mistaken for a strange new ninja at first. Then, he might learn about chakra and try to combine his own natural abilities with chakra - based techniques. For instance, he could use his punching power enhanced by chakra to defeat stronger opponents. Also, there could be a plot where he has to protect the Hidden Leaf Village from a threat that is related to his own world, like an evil Sonic - like character who has also found a way into the Naruto universe.
A 'Knuckles the Echidna is Naruto fanfiction' could center around Knuckles' journey of discovery in the Naruto world. He may start off being completely out of place, not understanding the ways of ninjas. But as he spends time there, he begins to respect their values and skills. There could be a sub - plot about him teaching the ninjas some of his own combat moves in return for learning about ninjutsu. And of course, there would be a lot of action - packed scenes where he shows off his physical prowess against the various villains and threats in the Naruto universe, all while forming deep friendships with the characters like Naruto, Sasuke, and Sakura.
Yes, there are some. You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Knuckles the Echidna Naruto' and you might find some interesting crossovers where the writers blend the unique characteristics of Knuckles from Sonic with the Naruto universe in creative ways.
Knuckles is a red echidna. His origin story has him as the last of his kind on Angel Island. He was tasked with guarding the Master Emerald. He was often tricked by Dr. Eggman into believing Sonic was a threat to the Emerald. He's a strong fighter and his isolation on the island led to his somewhat gullible nature in the face of Eggman's deceptions at first.
One key element is his heritage as an echidna from a vanished tribe. Another is his solitary existence on Angel Island with the all - important task of protecting the Master Emerald. Also, his initial naivete which led to him being deceived by Eggman, especially when it came to his interactions with Sonic. These are the main aspects of his origin story.
It could completely change the direction of the plot. If the echidna is released, it might bring a new type of power or threat into the Naruto world that the characters have to face.
In Naruto fanfiction, an echidna sealed could potentially be a source of great power. It might be sealed by an ancient shinobi for various reasons, like to prevent its destructive abilities from being unleashed. Maybe it has unique chakra-related powers that could be harnessed if the right conditions are met in the story.
I'm not entirely sure specifically what that particular fanfiction is about as there could be many interpretations. It might be a story that involves characters named Percy and Echidna in some sort of fictional scenario created by a fan. It could potentially be an adventure - based story, or perhaps a story exploring their relationship in a unique way.
It might involve Naruto having some Targaryen - like features. Maybe he has the signature Targaryen silver hair and purple eyes. And of course, there could be dragons involved. Naruto could form a special bond with a dragon, similar to how he bonds with his summons in the original Naruto series.
A 'Naruto is Cell fanfic' might involve some sort of experiment gone wrong. For example, Orochimaru could be trying to create a new type of super - soldier and accidentally merges Naruto with Cell's DNA. This would lead to Naruto having to come to terms with his new form and powers while still trying to protect his village.
Well, it might involve a crossover event where Naruto is transported to the Bleach universe and is influenced by Aizen. He could then use Aizen's knowledge of reiatsu and spiritual manipulation to enhance his own chakra abilities. Or perhaps Aizen's influence causes Naruto to see the hidden power structures in his own world differently, leading to a revolution of sorts in the Naruto universe.
Maybe Naruto could be a foreign warrior who gets involved in the Crusades. He might use his ninja skills to fight in the battles, like using his shadow clone jutsu to outnumber the enemies on the battlefield.