Danzo could be a great antagonist in this fanfic. He was always power - hungry and had his own secretive ways. He might see the five pronged seal as a way to control Naruto or to use his power for his own dark purposes. He could try to manipulate Naruto or those around him to keep the seal in place or even make it stronger for his own gain.
It could be a new character, like a young genin who has a natural affinity for seals. This character stumbles upon the mystery of the five - pronged seal during a routine mission in an old, abandoned temple. They are curious and determined, which drives them to uncover the secrets of the seal.
One possible plot could be centered around a young ninja who discovers an ancient scroll related to the five - pronged seal. This ninja, perhaps an outcast in their village, starts to study the seal in secret. As they delve deeper, they find that the seal has a connection to a long - forgotten power that could either save or destroy the ninja world. They must then decide whether to share this discovery or keep it hidden while facing the moral dilemma and the threat of those who would misuse the power if they knew about it.
It could be an old enemy of the village who has been waiting for the seal to break. Maybe someone who was imprisoned by the same seal long ago and now wants revenge on the village for sealing them away.
One idea could be exploring how the five pronged seal affects Naruto's chakra in unique ways that were not shown in the original series. Maybe it gives him new abilities or limitations that he has to overcome.
It could be a rogue Kumo ninja who wants to steal Naruto's seal - mastering knowledge for his own evil purposes. Maybe he wants to use the seals to take over Kumo or even the whole ninja world.
A rogue shinobi who has found a way to corrupt the Reaper Death Seal and use it for his own evil purposes. He could be stealing the souls of innocent people instead of using it as a last - resort jutsu like it was intended.
The Organization in the Claymore world could be the main antagonist. They already have a lot of secrets and do some morally ambiguous things. If Naruto shows up and starts changing the status quo, like teaching Claymore warriors to be more independent, the Organization might see him as a threat and try to eliminate him.
It could be a rogue ninja who was once a student of Orochimaru and has now developed his own dangerous jutsu. He wants to take over the ninja world and believes the old ways are holding everyone back.
Orochimaru could be a great antagonist. He might want to use Shenron's power for his own dark experiments. He could try to steal the dragon balls and manipulate the wishes to gain immortality or create an army of powerful, immortal ninja.
It could be someone who opposes Naruto's newfound admiration for Ganondorf. Maybe a traditionalist ninja who thinks Naruto is straying from the true ninja path by getting influenced by Ganondorf.