Ron could be another important ally. His loyalty and courage would be crucial. He might be the one to act as a decoy sometimes, drawing attention away from Harry when he is on a dangerous spying mission. Also, Ron's ability to blend in with the wizarding crowd could help Harry gather information without being too conspicuous.
Dumbledore, even if he's passed away, could still be an ally through his memories or portraits. His wisdom and knowledge of Voldemort would guide Harry in his spying efforts. And there could be other unexpected allies, like some of the centaurs or house - elves who have their own reasons to oppose Voldemort and are willing to help Harry in his dangerous mission.
Hermione could be one of his allies. Despite her usually rule - following nature, she might side with Harry if she sees the merit in his rebellion. Also, Ron would likely be there, as he has always been by Harry's side through thick and thin.
One possible plotline could be Harry using his unique access to Hogwarts to pass false information to Voldemort's followers. For example, he might tell them that a powerful magical artifact is hidden in a certain place, leading them on a wild goose chase while the Order of Phoenix prepares for a real battle.
Hermione would most likely be one of his top allies. She's smart and well - read in wizarding law, so she could help Harry build his case. Ron would also be there for moral support and to offer his own unique perspective on things.
Ron could be Harry's ally as well. Despite his sometimes clumsy nature, he's loyal and has his own areas of expertise, like wizard chess which could be metaphorically applied to some strategic decision - making in the Ministry. Additionally, some of the younger, more progressive Ministry employees who are inspired by Harry's heroics could also side with him and be his allies in any changes or projects he undertakes within the Ministry.
Daenerys Targaryen could potentially be an ally. She is open - minded about different powers and has her own dragons. Harry's magic could be seen as another powerful asset. And Jon Snow, being a noble and brave character, would likely welcome Harry's help in the fight against the White Walkers and might offer his own military expertise in return.
Maybe some unexpected allies could emerge. For example, a centaur who has witnessed the unjust actions of the court might come forward to help Harry. Or a goblin who has knowledge of the court's financial misdeeds could offer assistance. Harry's reputation for being a hero could attract all sorts of beings who want to see justice served in the court.
I think Hagrid would be a great ally. He loves all magical creatures and would be very accepting of Harry's new form as a winter spirit. He could introduce Harry to some winter - adapted magical beasts that could help him. Also, some of the older students like the Weasley twins could be allies. They would be excited about Harry's powers and use their creativity to come up with new ways to use his winter magic for fun and for the good of the school.
Hedwig could be a potential ally. She could carry messages to Harry's friends at Hogwarts, alerting them of his situation. Even though she is just an owl, she has shown loyalty and intelligence in the original series.
Ron would also be important. His loyalty to Harry is unwavering. He might be the one who bravely volunteers to go on the most dangerous part of the rescue mission, perhaps facing off against some of Voldemort's most feared Death Eaters.
There are many ways this could happen in fanfic. One way is that Harry uses his connection with Voldemort's mind. Since Harry has a link to Voldemort's thoughts, he might be able to pick up on Voldemort's doubts about Snape. And then Harry starts to investigate Snape further. He might recall some strange actions of Snape in the past, like his ambiguous loyalty during certain battles or his secret meetings with some unknown figures. Combining all these, Harry eventually realizes that Snape is a spy.