One idea could be the chaos soldier having a unique jutsu that disrupts the normal chakra flow in the Naruto world. Maybe it causes unexpected alliances to form as everyone tries to figure out how to counter it.
Perhaps a chaos mage could create chaos within the ninja academies. They could make the training exercises go haywire, like turning simple target practice into a wild chase where the targets move on their own and attack the students. This would force the students, including Naruto, to think on their feet and develop new skills to deal with the unexpected chaos. It could also be a story where the chaos mage tries to use their magic to rewrite the history of the ninja world, but the ninja fight back to preserve their heritage.
One plot idea could be Naruto being transported to the world of Dragon Slayers and having to learn their magic to get back home. He might combine his ninja skills with the new magic he acquires. Another could be a team - up between Naruto and Natsu to fight a common enemy that threatens both their worlds. Maybe a dark force is trying to merge the Naruto universe and the Dragon Slayer universe and they have to stop it.
One interesting plot idea could be a new and powerful villain emerging in the 'naruto of chaos fanfic' world. This villain could have a unique ability that challenges Naruto and his friends in ways they've never faced before.
One idea could be a super soldier from another land coming to the Naruto world with unique jutsu that no one has seen before. This could create a lot of mystery and excitement as the Naruto characters try to figure out this new threat or ally.
One idea could be that Naruto accidentally releases an ancient and powerful jutsu that disrupts the chakra balance in the ninja world, causing chaos among the villages. Another could be Naruto being possessed by a mischievous spirit that makes him act out of character and start random battles. Maybe Naruto tries a new and untested training method that goes horribly wrong and creates chaos in Konoha as his powers go haywire.
A plot could involve them getting lost in a mysterious, enchanted forest. In this fanfiction, they have to rely on each other to find their way out, and along the way, they discover hidden powers within themselves and form a stronger bond.
One plot idea could be Percy being sent on a secret mission by the Chaos forces to infiltrate an enemy stronghold. He uses his skills and wits to gather intelligence without being detected.
A possible plot for 'Percy is a Son of Chaos' fanfiction could be Percy being sent on a mission by Chaos itself. This mission could be to restore balance in a part of the universe that has been thrown into chaos (ironically) by some dark force. Along the way, he teams up with some unlikely allies, some of whom are also children of primordial entities. They all have different motives and powers, and Percy has to learn to work with them while also coming to terms with his own identity as a son of Chaos.
One idea could be that Percy has unique powers given to him by Chaos. For example, he might be able to control the very fabric of the universe in small ways. Maybe he can manipulate time on a very limited scale, like slowing it down during a fight to gain an advantage.
One idea could be Percy facing a new chaos - themed villain who can manipulate time in a disorderly way. Percy has to find a way to break the time - loops the villain creates.