Who might help Harry break out of Azkaban in the fanfiction?

It could be Sirius Black. Since he has his own experience with Azkaban, he might know some secrets about the place. He could return in some form within the fanfiction and assist Harry in his escape, maybe by leading him through some hidden tunnels or using some special skills he developed during his time in prison.

Maybe he uses some powerful magic spells that he has learned secretly. For example, the Patronus charm could be used to fend off the Dementors which are the main guards in Azkaban. He might also get some unexpected help from his friends or some mysterious characters within the fanfiction world.

It could be Dumbledore. He has great power and knowledge. He might have some secret plan all along. He could use his influence and magic to enter Azkaban and free Harry, especially if he discovers that Harry is wrongly imprisoned.

Perhaps Voldemort has some inside help. He could have bribed or threatened one of the guards or even a Ministry official who has access to Azkaban. This person could then help him get in and break Harry out. Or he might have found a secret passage into Azkaban that the Ministry doesn't even know about, and he uses that to his advantage.

There could be some new characters introduced in the fanfic. Maybe a powerful wizard from a far - off land who has heard of Harry's plight and decides to help. Or perhaps a group of outcasts in the wizarding world who see Harry as a symbol of their own struggle against the unjust system and come to his aid.

Obviously, Harry Potter himself is a key character as the story is about his release from Azkaban. Dumbledore is likely to be important too. He has the power and influence within the wizarding world to potentially free Harry. His wisdom and knowledge of the situation would play a big role.

It could be a jealous classmate from Hogwarts. Someone who has always been in Harry's shadow and finally sees an opportunity to get rid of him. This person might be a Slytherin who has connections with some dark wizards outside of school and they work together to frame Harry.

Neville could be another helper. He has become quite skilled in herbology. He could help Harry by creating a magical garden around the house. The plants in the garden could be used for protection, like thorny bushes that keep unwanted visitors away, or for providing ingredients for household potions.

Dumbledore might help from beyond the grave, in a sense. Harry could discover some of Dumbledore's old notes or memories that provide crucial insights into building a powerful and controlled bomb. And perhaps some of the more eccentric professors at Hogwarts, like Professor Flitwick, could offer their expertise in charms which might be needed for the bomb's construction.

Maybe a jealous wizard or witch within the Ministry of Magic. They might be envious of Hermione's popularity and influence among the younger wizards. So they fabricate evidence against her to get her locked up in Azkaban.