There could be a group of dark wizards who are secretly operating within the Ministry itself. They oppose Harry's alliance with the Ministry because they fear that Harry will expose their illegal and immoral activities, like illegal potion - making or dark - magic experiments.
Another possibility is that some of the former Death Eaters who have managed to escape punishment and are now trying to disrupt the Ministry - Harry alliance. They might want to take revenge on Harry and the Ministry for their defeat in the war and will stop at nothing to create chaos and break their new - found cooperation.
The main antagonists could be the top - ranking officials in the Ministry who are desperate to hold on to their power. They would likely use all means at their disposal, including dark magic and underhanded tactics, to stop Harry and his allies.
Well, one possibility could be that Harry realizes the Ministry has some good intentions that have been misconstrued. He might ally with them to fight a common enemy, like a new dark wizard threat that is more powerful than Voldemort. Harry could use his influence within the wizarding community to bridge the gap between the Ministry and the people who have lost trust in it.
The school bully could be a main antagonist. He might pick on Austin for being a singer and think he's too full of himself, or he could target Ally for being a bit of a nerd. Another could be a jealous rival singer in the school who wants to take Austin's place and will do anything to undermine him. And there could also be a strict teacher who doesn't believe in their music dreams and tries to stop them from performing at school events.
Maybe it could be a rival music producer who tries to use their new baby situation to create negative publicity for them. They might spread rumors about how having a baby will ruin their music careers.
A group of jealous students could be the main antagonists. They might be envious of Harry's natural talent and the attention he gets from the teachers. So, they try to sabotage his progress at the gifted school by setting him up to get in trouble or stealing his study materials.
Maybe a group of anti - magic fanatics within SHIELD itself. They see Harry's magic as a threat and try to undermine him at every turn. They could be secretly working with external forces that also oppose the use of magic in the world of SHIELD. Harry would have to prove that his magic can be an asset rather than a liability.
It could be a group of dark wizards who don't want Harry to succeed in becoming a cursebreaker. They might be using dark curses themselves to cause chaos in the wizarding world, and they see Harry as a threat to their plans. So they try to stop him at every turn, whether it's by setting traps or sending out cursed creatures after him.
Maybe there are some ancient dark wizards that Iskandr has a history with. These wizards could see Harry as a threat because of his potential, especially with Iskandr's training. They might emerge from hiding to try and stop Harry from reaching his full power, fearing that he and Iskandr together could disrupt their long - planned evil schemes.
There could also be a new group of supernatural beings, perhaps a cult that worships dark magic. They might target Hellsing because of their power and the fact that Harry, with his wizarding abilities, is now part of the organization. This cult could be trying to summon some ancient and extremely dangerous entity, and Hellsing, with Harry's help, has to stop them.
There could be a secret society within the wizarding world that has long opposed the Knight Templars. They see Harry's new - found connection to them as a revival of an old threat. They try to undermine Harry and his attempts to bring the Templar values into the wizarding world by spreading false rumors and creating obstacles for him at every turn.