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.
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 potential character could be a new student who arrives at Hogwarts with a mysterious past. He shows extraordinary magical abilities that seem a bit too dark for the normal wizarding world. Another could be a distant relative of Draco Malfoy. Since the Malfoys have a history with the dark arts, it wouldn't be too far - fetched for one of them to be revealed as the heir of Sauron. Or perhaps an old wizard who has been in hiding for centuries and resurfaces as the heir of Sauron.
Bellatrix Lestrange, if she had survived the Battle of Hogwarts. She was extremely powerful and deranged. She could rule the wizarding underworld with an iron fist, using fear and torture to keep her subordinates in line. Her loyalty to Voldemort could be transferred to her own self - serving criminal empire.
Fred Weasley could also be seen as a ladies' man. He's funny, outgoing, and always up for a good time. Fanfiction could explore how his humorous and mischievous nature draws the girls to him. He might be the type to play pranks on the girls just to get their attention and then charm them with his witty remarks.
In the Harry Potter fanfiction, the 'thief of time' could be a character that has been overlooked or underestimated. It could be a young wizard who discovers a powerful but dangerous magic related to time. He might not fully understand the consequences of his actions and accidentally becomes the 'thief of time'. Or it could be a shape - shifter who uses different forms to steal time without being detected easily. They could be stealing time from important magical ceremonies or from the lives of key characters in the story.
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.
There could also be a mysterious outsider from another land. They've heard about the power of the Naruto world's bloodlines and come to steal them. This outsider might have their own motives, like using the bloodlines to strengthen their own people back in their homeland. They would be a completely new and unpredictable element in the Naruto universe, making for an interesting story as the characters try to figure out who this unknown thief is and where they come from.
It could be that he has been wronged by the wizarding society. So, in a form of rebellion, he decides to become a thief. He might steal from those who he thinks are corrupt or unfair. For example, if the Ministry of Magic has been unjust to him or his loved ones, he could target them or their allies. Another possibility is that he is influenced by a powerful and devious character who convinces him that stealing is a way to gain power or freedom.
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.