Another potential enemy could be a group of pure - blood supremacists who don't like the idea of the White Knight, who might be a symbol of change and equality in the wizarding world. They would try to undermine the White Knight's efforts to make the wizarding world more inclusive.
There could be a new dark wizard or witch who is jealous of the Potter family's legacy. They might target Harry Potter's daughter to try and bring down the family name and prove their own power.
The Death Eaters could still be a major threat. Even with Voldemort gone, some of them might be trying to revive the dark ways and see the wizard king as a big obstacle in their path.
The obvious enemies could be the Ministry of Magic. If Harry is stealing things, even if for good reasons, they would see him as a criminal. The Aurors would be sent after him. Another potential enemy could be some of the dark wizards who might want the same items that Harry is after. They would not want Harry to get in their way and would try to stop him or even capture him to get information on the whereabouts of the valuable items.
One interesting plotline could be the development of a new magical ability in the White Knight that helps Harry and his friends in their fight against Voldemort. For example, the White Knight might discover a way to manipulate time in a small area, allowing them to undo some of Voldemort's recent evil deeds.
Voldemort or his remaining Death Eaters could be the main enemies. They would see Harry's new blade master abilities as a threat. Another potential enemy could be a dark wizard from a foreign land who is jealous of Harry's power.
Alien races that are envious of the Earth - born magic could be enemies. They might see Harry and the wizards as a threat to their own power and dominance in the universe. Also, there could be dark wizards who have escaped to space to avoid the law on Earth and continue their evil deeds, now with a new set of space - related challenges and opportunities.
Voldemort would still be a major enemy. But with Kratos raising Harry, Voldemort might face a much more challenging opponent. Also, any dark wizards or creatures that oppose Harry would be in trouble. Kratos wouldn't tolerate any threats to Harry, so even the Death Eaters would have to be extra careful. Another potential enemy could be those in the wizarding world who oppose Kratos' methods of raising Harry, seeing them as too brutal or un - wizard - like.
Some of the dark wizards who are looking for a new source of power might target Harry. They might think that by capturing or controlling him, they can access the powers of Trigon. There could also be entities in other dimensions that see Harry as a key to opening portals between worlds and want to use him for their own malicious purposes.
The Ministry of Magic would likely be an enemy. They are all about maintaining order and the Demon Prince's actions might be seen as a threat to that order.
A new dark wizard could rise. This wizard might be jealous of the fame and power that Harry has, and seeing his daughter as an extension of that, decides to target her. Maybe this new dark wizard is seeking to gain control over the wizarding world and sees her as a key obstacle in his path.