Common themes include self - discovery. Percy has to figure out how being the Son of Echidna fits into his life. Also, there's often a theme of conflict. This could be conflict with other characters who might be suspicious or jealous of his new status. And family is also a theme, as he has to deal with the implications of having Echidna as a parent in a world where his relationships with other characters like Poseidon are already complex.
Yes, there are quite a few. You can start by looking on fanfiction websites like Archive of Our Own or FanFiction.net. Just search for 'Percy Jackson Son of Echidna' and you'll find a variety of stories, from action - packed adventures to more character - focused ones.
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.
I'm not sure who the main characters are as I haven't read it. But it could be a brave echidna warrior who leads his troops into battle. Maybe he has some special abilities or a strong sense of honor.
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.
One common theme is loyalty. Echidna characters often show great loyalty to their clans or comrades in the fanfictions. For example, they might fight to the death to protect their fellow echidnas.
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 sure specifically as I haven't read this exact story. But generally, it might be about the relationship between the echidna and the shade tree, perhaps how the echidna uses the tree for shelter or some sort of adventure that involves the two.