It could be a powerful demon lord from a dark anime universe. This demon lord might seek to conquer all the anime universes in the 'anime war infinite' setting. He could have an army of dark creatures and powerful magic at his disposal, making him a formidable foe.
Maybe the main antagonist is a jealous rival. This rival is envious of her abilities and status, so she uses a forbidden magic to turn her into a card. The rival then tries to take her place in the story, but her friends start to suspect something is wrong and begin to investigate.
It depends on the specific story. Different stories have different antagonists. Sometimes it could be a villain with evil intentions, and other times it might be a character with opposing goals to the protagonist.
An antagonist is basically a character or a force that opposes the main character or protagonist. They create conflicts and obstacles for the hero to overcome.
Animation was an art form, usually referring to comics, illustrations, animations, games, and other media forms that were adapted or mixed. It had a distinct artistic style and a unique form of expression that could attract a large audience. Comics are usually for entertainment purposes, but they can also be educational, cultural, or science-related. Comics were very popular around the world, not only in Asia and Europe, but also in America and Africa.
It could be someone from the Naruto universe who doesn't like Naruto's newfound fascination with Aku. For example, Danzo might see Naruto's interest in Aku as a threat to the stability of the village and try to stop Naruto from further exploring Aku - related things. So, Danzo could be the main antagonist in this case.