In 'harry is an apprentice fanfiction', apart from Harry, there might be other apprentices too. They could be his friends or rivals during his apprenticeship. Also, we can't rule out the appearance of some of the main antagonists from the original series, as they might try to interfere with Harry's apprenticeship journey.
Another possible main character could be a new villain. Since Harry is in a new role as an apprentice, there could be someone who wants to steal the secrets of Ollivander's wand - making. This villain could be a dark wizard or a rogue wizard who has his own motives for wanting to control the wand - making process. Harry would then have to protect Ollivander and the shop from this threat.
Obviously, Naruto and Hayate would be the main characters. Naruto is the protagonist who will be learning from Hayate.
Obviously, Naruto and Hiruzen would be the main characters. Naruto as the apprentice and Hiruzen as the mentor.
Obviously, Naruto and Anko would be the main characters. Naruto, the energetic and determined ninja, and Anko, the somewhat eccentric and skilled kunoichi.
Well, obviously Harry Potter himself is a common character. And his mentor, who could be an original character created by the fanfiction author or an existing character from the wizarding world like Albus Dumbledore in a different role as a more hands - on master.
Another possible candidate could be Tom Riddle before he fully became Voldemort. He was already exploring the darkest corners of magic at a young age. The idea of the Sith and their power might attract him. He could see the Sith as a means to an end in his quest for immortality and ultimate power. As a Sith apprentice, he could combine the knowledge of the Dark Side of the Force with his own wizarding knowledge, creating a truly formidable and terrifying entity.
It's hard to say. Harry has a natural talent and courage, which could help him succeed. But Draco is well - versed in the pure - blood magic traditions and might have an edge in some aspects. Snape might be tougher on Harry due to their past, but that could also make Harry more determined. So it could really go either way depending on how the story is written.
Anko might also be involved in the story. She has her own unique relationship with Yugao and could potentially interact with Naruto. Maybe she gives Naruto some tough love or challenges him in a way that Yugao's teaching methods don't cover. And of course, Iruka sensei could also show up to check on Naruto's progress and have some interactions with both Naruto and Yugao.
Obviously, Harry Potter himself. And there could be Dumbledore, who might guide Harry in this new path related to Merlin. Also, Hermione and Ron could be there, either helping Harry or being a bit skeptical about this new adventure.
Harry Potter himself is also very popular. He could be seen as an older, wiser apprentice passing on his knowledge of fighting dark magic to the new generation of students. His adventures against Voldemort give him a lot of experience to share.