Another potential villain could be a corrupted Hogwarts professor. They could be secretly working against Harry, perhaps trying to steal his power or knowledge. Harry would have to use his wits and his own magical abilities to expose and defeat this traitor within the walls of Hogwarts without relying on the help of other students or the other professors.
Voldemort would still be a likely villain. He is the main antagonist in the original series and his threat to Harry is always present. Even if Harry is trying to save himself, Voldemort's power and his desire to kill Harry would make him a formidable foe.
The Akatsuki could be potential villains. They are always on the lookout for powerful beings or things that can help them achieve their goals. If the OC has something they want, like a special chakra or a unique ability, they would be a threat. Another could be rogue ninja from different villages who see the OC as an easy target or a means to get something valuable.
Well, aside from Voldemort, there might be corrupt elements within the assassin organization that raised Harry. They could see his magic as a threat to their power and secrecy. Also, there could be some dark wizards who team up with the assassin enemies of Harry. These villains would be more complex as they combine the danger of dark magic with the stealth and combat skills of assassins. And there could be a new character, perhaps an assassin who was once a friend but turns bad due to jealousy or a thirst for power, creating a more personal and dangerous threat to Harry.
The Death Eaters are a likely choice. They might target Susan Bones because of her family's connection to the wizarding world. For example, her aunt Amelia Bones was a well - known figure, and the Death Eaters could be after something related to her or the Bones family in general.
It could be Death Eaters who have a new plan. They might want to create chaos in the Muggle world by targeting the Queen. They see her as a symbol of Muggle power and order, so by attacking her, they hope to disrupt the Muggle - wizard relationship.
It could be some Death Eaters who have made a deal with a Wakandan traitor. They might want to steal Wakanda's vibranium to make powerful dark magic items. The Death Eaters' dark magic would pose a serious threat to Wakanda's peace and stability.
It could be some of the remaining Death Eaters. They might target Amelia Bones because she is a powerful and important figure in the Ministry of Magic. Her knowledge and influence could be a threat to their plans of resurrecting Voldemort's ideology or causing more chaos in the wizarding world.
One potential villain could be Orochimaru. He might have an interest in Naruto's sister for her unique chakra or some genetic trait. He could be using her as a pawn in his experiments to gain more power or knowledge about the Uzumaki clan.
In the wizarding world, there might be some jealous wizards who don't like Harry's unique combination of powers. They could team up with dark forces, maybe some Death Eaters who are still lurking around, and try to bring Harry down. They might be envious of the attention Harry gets or fear his new - found powers will disrupt the traditional ways of magic.
One potential villain could be Voldemort from the Harry Potter world. He might see Harry's new alliance with Erza as a threat and try to destroy it. Also, there could be villains from Erza's world who are jealous of the power that Harry and Erza together possess.
One potential villain could be a rogue Death Eater who escaped justice. This Death Eater might see Teddy as a symbol of the new generation that he wants to destroy. Another could be a jealous wizard who is envious of Teddy's special abilities, like his Metamorphmagus powers, and tries to harm him. Harry would then have to fight these villains to protect Teddy.