Ron could also be a main character. He would be there for moral support and might accidentally come up with some useful ideas. Dumbledore could also play a role. He might have some secret knowledge about the egg and guide Harry in the right direction when it comes to hatching it and dealing with the hatched creature.
Hermione could be one. She might use her vast knowledge of magic to help Harry figure out how to hatch the egg. Another could be Hagrid. He has a lot of experience with magical creatures, so he could offer advice on taking care of the egg and the soon - to - be - hatched creature.
There could be a new character, a young wizard or witch from a different magical school who has some unique knowledge about eggs like this. They could cross paths with Harry and join him in his quest to hatch the egg. Also, Neville could be involved. He's grown a lot in his magical abilities and could contribute to the care of the egg and the new creature.
Neville could play a role too. He has a deep connection to the magical creatures, and he might be sympathetic to Harry's idea of hatching the basilisk. He could offer some advice on how to handle the hatchling based on his own experiences with plants and other less - dangerous magical beings. Also, he could be the one to stand up for Harry when others start to question his motives.
Maybe Harry discovers a magical egg. He has to keep it warm and protected. As he does so, he forms a special bond with the creature inside the egg. Eventually, it hatches into a rare and wonderful magical creature that helps him in his adventures.
Hermione and Ron would also be important characters. Hermione might be initially skeptical of Harry's newfound obsession with the Marauders. Ron, on the other hand, might be more easily swayed and join Harry in his attempts to be more like the Marauders.
A vampire hunter could be a key character. They might initially see Harry as a target too because of his association with the vampire. This would create a lot of tension as Harry and his mate have to either convince the hunter that they are not a threat or fight against them. And don't forget about Dumbledore (assuming this is in the Harry Potter universe). His reaction to Harry's new situation would be very interesting to explore.
Voldemort could be the main antagonist. Even though he's gone in the original story, in this fanfiction, he might be resurrected or his followers could be after the dragon. They might see the dragon as a powerful weapon to use against Harry and the wizarding world.
There could be his drill sergeant. A tough but fair character who pushes Harry to his limits. Maybe he has a name like Sergeant Thompson.
Well, in some cases, there could be minor characters from the original series who still interact with Harry on a limited basis. For example, Neville Longbottom might make an appearance. Even though Harry is alone for the most part, Neville could cross paths with him and have a brief conversation or exchange that has an impact on Harry's journey.
There could be Ron. He might be Harry's sidekick in the gambling adventures, either joining him in bets or trying to stop him when things get out of hand. Ron's loyalty would play a big part in their relationship within the story.
Ron might also be a main character. He could be initially skeptical of Harry's new powers but eventually come around and support him. He might even use his own skills, like his chess - playing strategy, to help Harry in battles or challenges related to his Dragonborn status.
Ron could also be a main character. He might initially be a bit confused or even jealous of Harry's new powers as an elf, but then come around to support him. His family, like the Weasleys, could also be involved, perhaps providing a different perspective on elves compared to the pure - blood wizarding families.