In the 'harry potter trained by kratos fanfiction', the main antagonists could be those who oppose the new power that Harry is gaining under Kratos' training. It could be certain pure - blood wizarding families who see Harry as a threat to their traditional ways. Also, there could be some sort of dark force that is awakened by the combination of Harry's magic and Kratos' influence, and this dark force becomes the central antagonist as it tries to destroy both Harry and Kratos.
It's hard to say for sure without reading the fanfiction. But it could be the usual suspects like Voldemort and his Death Eaters. However, with Kratos in the picture, there might be new antagonists from Kratos' world who see Harry as a threat now that he's being trained by such a powerful being.
Perhaps in this fanfiction, the main antagonists could be a combination of the dark wizards from the Harry Potter universe and some sort of ancient evil that Kratos has been fighting. Since Kratos is now involved with Harry, this ancient evil might target Harry to get to Kratos. And of course, Voldemort would still be a major threat, but he might be even more afraid of Harry now that he's being trained by someone as fearsome as Kratos.
In this fanfiction, there might be a group of wizards who oppose the idea of mixing magic with the skills taught by Hephaestus. They could be the antagonists as they try to prevent Harry from using his new - found skills. They might believe that this new form of magic is dangerous or against the traditional ways of the wizarding world. They could form an organization to oppose Harry and try to disrupt his training and any plans he has to use his skills for good.
Perhaps some traditionalist wizards in the Ministry of Magic. They might view Harry's training by snakes as a form of dark magic practice, even if it's not. So they become the antagonists, trying to arrest Harry or stop his training in some way.
In this fanfiction, it could be that Harry Potter, under Kratos' training, would develop a whole new set of magical abilities. Kratos' Spartan training methods might be applied to magic. For example, Harry could learn to use his magic in a more instinctive and immediate way, like how Kratos wields his weapons. Also, Harry's view on good and evil could be influenced by Kratos' own complex moral code.
The main characters would be Harry Potter and Batman. Harry Potter, the young wizard from the wizarding world, is the focus as he is being trained. Batman, the Dark Knight from Gotham, brings his skills and knowledge to the table. There might also be some appearances from other characters in the Harry Potter universe, like Hermione and Ron, who could react to Harry's new training. And in the Batman side, perhaps Alfred could also play a role, providing support or advice in the training process.
The main characters are Harry Potter and Thor. But it's possible that some other important characters from both universes could play a role. In the Harry Potter universe, Dumbledore might have an opinion on Harry's new training. And in the Thor universe, Odin could be aware of Thor training an outsider like Harry. Their reactions and interactions could add more depth to the story in this fanfiction.
Scarecrow could also be a main antagonist. His fear - inducing toxins could be a real problem for Harry. Harry would have to use his magic to counter the effects of the fear toxin and also figure out a way to stop Scarecrow from spreading it all over Gotham.
Another possibility is that there could be a magical creature that has some sort of grudge against Fawkes. This creature might see Harry as an obstacle because of his bond with Fawkes. It could be an ancient and powerful creature that has its own motives and goals that conflict with Harry and Fawkes' relationship.
The Thalmor could be great antagonists. Their strict control over magic and their anti - human beliefs could put them at odds with Harry. They might see his different form of magic as a threat to their power in Skyrim.
Voldemort or his followers might also be antagonists. Even if Voldemort is defeated in the original story, in this fanfiction, his remaining Death Eaters could see Harry's new power as something they can either use or must destroy. Or perhaps a new dark wizard inspired by Voldemort's ideology rises up against Harry.
One possible antagonist could be a corrupt wizard in a high - ranking position in the Ministry of Magic's financial department. This wizard might be trying to cover up his misdeeds and would see Harry as a threat to his scheme.