His relationship with Harry Potter could be very complex. They were enemies during their school years, but after Azkaban, they might find common ground. Maybe Draco realizes that Harry also had a tough time and they start to respect each other's struggles. They could end up working together on some project for the betterment of the wizarding world.
Another idea is that Draco becomes involved in some sort of underground magical movement. After Azkaban, he may be disillusioned with the established magical order. He could join a group that aims to reform or even overthrow the current power structures in the wizarding world, leading to all sorts of adventures and conflicts.
One possible fanfiction could involve Harry finding out that Draco was wrongly imprisoned in Azkaban. Harry might use his influence and his skills as an Auror to dig deeper into Draco's case. He could discover evidence that clears Draco's name, like finding out that Draco was framed by some dark wizards who wanted to get rid of the Malfoy family's influence. Then, Harry would have to fight against the bureaucratic system of the Ministry of Magic to get Draco released.
He might use the invisibility cloak. Harry could sneak into Azkaban unnoticed and then use magic to break Draco out of his cell. The cloak has served him well in the past, and it would be a simple yet effective way to get past the guards.
One consequence could be a change in the public's perception of Hermione. Some might see her as a hero for standing up against an unjust imprisonment, while others might view her actions as traitorous, especially if they believe Draco was truly guilty. This could create a divide among the wizarding community.
Well, perhaps Hermione discovers some dark secret of Draco's that she can use as evidence to frame him for a crime, leading to his incarceration in Azkaban. Maybe it has something to do with his family's past actions that she twists to make him look guilty.
One possible plot could be that Harry discovers some new evidence that proves Draco's innocence. Maybe there was a frame - up by some dark forces within the wizarding world. Harry, being the hero he is, feels compelled to act and uses his influence and skills to break Draco out of Azkaban. This could lead to them having to go on the run together, hiding from the authorities while they try to expose the real culprits.
In this kind of fanfiction, it could happen in various ways. Maybe Hermione discovers some evidence that Draco was wrongly accused. For example, she might find that certain spells were cast on Draco to make him seem guilty when he actually wasn't. So she uses her intelligence and knowledge of magic to expose the truth and save him from Azkaban.
The plot could start with rumors reaching Harry that Draco is being unjustly treated in Azkaban. Harry, being the hero he is, decides to investigate. He uncovers a conspiracy within the Ministry of Magic that is trying to keep Draco locked up for political reasons. Harry then uses his connections, like his friendship with Neville who now has some influence in the Ministry, to get a hearing for Draco. During the hearing, Harry presents the evidence he has found, which includes magical artifacts that prove Draco's innocence, and Draco is finally released.
Hermione might become more morally ambiguous. Normally she is a very just and rule - following character, but by tricking Draco into Azkaban, she steps into a grey area. She could start to question her own actions and feel guilty.