Sasuke could also be a potential antagonist in this fanfiction. He might be a rival knight who has been influenced by a dark force. He believes in a more cut - throat approach to achieving power and status in the knightly world. Naruto, on the other hand, follows the path of honor and kindness. Their conflicting ideologies lead to many battles and confrontations as Naruto tries to bring Sasuke back to the right path.
It could be Orochimaru. In the medieval knight setting, he might be a dark sorcerer who wants to use the power of the knights for his own evil purposes. He could be trying to steal the holy relics of the kingdom which are said to grant great power, and Naruto, as a knight or someone with knight - like qualities, has to stop him.
Madara could be the main antagonist. He might be a powerful warlord in the medieval knight world. He desires to conquer all the kingdoms and bring them under his rule. Naruto, with his values of justice and friendship, stands against him. Madara would use his brute force and strategic mind to try and defeat Naruto and his allies, who are upholding the code of chivalry.