If Harry Potter were sent to Azkaban in fanfiction, it could be a very dark turn of events. He would likely be wrongly accused, as he often is in the face of Ministry corruption. His time in prison might involve him using his magic in secret to resist the Dementors, and it could also lead to an uprising within Azkaban by other inmates who believe in his innocence. It could also prompt his friends to stage a dangerous rescue mission.
In fanfiction, if Harry Potter were sent to Azkaban, it would be a huge deviation from the original story. He would likely face extreme hardships. The Dementors there would constantly drain his happiness. His friends, like Hermione and Ron, would probably try everything to prove his innocence and break him out. It could also lead to a situation where Voldemort might gain more power without Harry being able to oppose him freely in the wizarding world.
In such a fanfiction, perhaps Dumbledore would immediately start an investigation to prove Harry's innocence. He might call in old favors from various magical beings. Hermione would likely be at the forefront of researching ways to break Harry out legally, using her vast knowledge of magical laws.
Often, the plot develops with a sense of mystery. His friends would start to investigate what really happened to get him sent there. There would be a search for evidence to prove his innocence. Meanwhile, Harry in Azkaban might discover some dark secrets about the prison itself or about those who sent him there.
The story could develop in many ways. One way is that Harry starts to lose hope in Azkaban, but then he finds a glimmer of something that gives him the strength to fight back. Maybe he discovers a hidden passage or an ally among the inmates. Another way is that the outside world starts to change without Harry. Voldemort could be making more moves, and Hermione and Ron have to step up in different ways to deal with it while also trying to free Harry.
If Harry has any special magical abilities or items that were overlooked, he could use them. For instance, if he still has the Marauder's Map, he might be able to find hidden passages in Azkaban to communicate with the outside or find evidence within the prison that clears his name. Also, his relationship with magical creatures like the Thestrals might come in handy. If they can be made to testify or help in some way, it could be a way to prove his innocence.
If Harry is sent to Azkaban in fanfiction, it would be a huge shock to the wizarding world. In Azkaban, the dark and gloomy environment would take a toll on him. But Harry has a strong will, so he might try to resist the effects of the Dementors. His Gryffindor courage would be put to the ultimate test. And he may discover some secrets about Azkaban while he's there, which could lead to a whole new plotline in the fanfiction.
One possible scenario in such a fanfiction could be that Harry is wrongly accused of a serious crime and sent to Azkaban. Snape, who has always had a complex relationship with Harry, might initially believe in his guilt due to their past animosity. However, as the story unfolds, Snape could start to suspect that there is more to the situation. He might begin his own investigation, secretly at first, to find out the truth behind Harry's imprisonment. This could lead to a series of events where Snape has to face his own prejudices and also deal with the political situation in the wizarding world that allowed Harry to be sent to Azkaban so easily.
To survive in Azkaban, Harry would need to keep his mind active. He could recall all his happy memories to counter the Dementors. His knowledge of magic could also be useful. For example, he could try to create some protective spells around his cell. And he might get some unexpected help from the guards or other mysterious forces within the prison.
In such a fanfiction, the plot might involve false evidence being planted against Harry. Maybe someone uses dark magic to create the illusion that Harry has committed a serious crime, like using an Unforgivable Curse. The Ministry of Magic, being quick to judge, sends him to Azkaban without a proper investigation. Harry would then have to find a way to prove his innocence from within the prison, perhaps with the help of his friends who believe in him and are secretly working on the outside to clear his name.