Voldemort could still be a potential villain even in 'Harry Potter leader fanfiction'. Maybe he returns in a different form or has some followers who are still causing trouble while Harry is trying to lead the wizarding world into a new future.
In some cases, a corrupted Ministry of Magic official could be the villain. They might oppose Harry's new leadership ideas and try to undermine him at every turn. They could be secretly in league with dark forces or just be power - hungry and see Harry as a threat to their own authority within the wizarding world.
A new dark wizard could emerge as a villain. This wizard might be jealous of Harry's leadership and popularity. He could start causing chaos by spreading dark magic and turning some wizards against Harry's leadership, creating internal strife within the wizarding world.
Another possibility is that the heiress could be a new character entirely, created by the fanfiction author. She could be from a foreign wizarding family that has a claim to something in the British wizarding world. This new character could bring in different cultural elements of magic and challenge the traditional ways of the Hogwarts - centered wizarding society.
Another possibility is a reformed dark wizard. Someone who has seen the error of their ways and now uses their in - depth knowledge of dark magic to teach students how to defend against it. This character would have a very interesting backstory, having once been on the wrong side but now using their experiences to help the next generation of wizards in the DADA class.
A long - lost relative of Sirius Black could be a shapeshifter. Since the Blacks had many secrets and were involved in a lot of dark magic in their family history, it would be believable for a hidden relative to have this unique ability.
Perhaps a new character could be introduced as the 'kingpin'. This character could be an older, more experienced wizard who has been in the shadows for a long time. They might have some ulterior motives and a different view on the wizarding world's politics compared to Dumbledore or Voldemort.
A potential godmother could be a long - lost relative of Lily Potter. Maybe a sister who was thought to be dead but actually survived and has been living in seclusion. She would be very powerful and have a strong connection to Harry through his mother.
One possibility could be Morgana. In some interpretations, she has powerful magic and could be reimagined as a more benevolent Goddess of Magic in the Harry Potter universe. Another could be a completely new character created specifically for the fanfiction, perhaps an ancient witch who has been watching over the wizarding world since its inception.
Hermione could be a great magical guardian in fanfiction. She's smart and resourceful. With her vast knowledge of magic, she could protect Harry in many ways, like using her spell - casting skills to fend off dark wizards.
A potential guardian could be Sirius Black's spirit. Even though he died, his love for Harry could be so strong that it allows his spirit to act as a guardian. He could appear to Harry in times of need, give him advice, and even use his limited spectral powers to protect Harry from minor threats.
An unknown wizard from a far - off land could be a thief in Harry Potter fanfiction. This wizard could come to Hogwarts or the wizarding world of Britain with the intention of stealing unique magical items that are not found in their own land. They would bring a sense of mystery and a new cultural perspective to the story.
He could meet an Egyptian wizard who is an expert in ancient magic. This wizard could teach Harry a great deal about the history of magic in Egypt.