One possibility could be that the wizarding world turns on Harry after the war. Maybe they start to fear his power and influence. They could spread false rumors about him being a dictator in the making. His friends might be pressured to turn away from him, and he would be left alone, feeling betrayed by those he fought for.
One possible plotline could be that some of the former Death Eaters who were pardoned as part of the post - war reconciliation secretly plot against Harry. They might spread false rumors about him misusing his power or being a threat to the wizarding world again. Another could be that some of his own friends turn on him out of jealousy. Maybe they feel overshadowed by Harry's continued fame and hero status and start to believe the lies being spread about him.
It could be some of the pure - blood supremacists who were biding their time. Even though the war was over, they might still resent Harry for his role in defeating Voldemort and decide to get revenge by making it look like he betrayed them. Another possibility is some of the Ministry officials who were corrupt and didn't want Harry's influence around.
It could be Ron. Maybe he starts to feel that Harry has changed too much after the war and is no longer the friend he once knew. He might be influenced by outside forces or his own insecurities. Another possibility is Hermione. If she gets too involved in the new Ministry politics and starts to believe that Harry's actions are not in line with the new wizarding order, she could turn on him.
The Ministry of Magic could be the ones to betray Harry. They might try to use Harry as a pawn in their political games, and when Harry realizes this, he loses faith in the so - called good side. Voldemort then takes advantage of Harry's disillusionment and convinces him to join.
In this fanfic, Harry might be betrayed by the Order of the Phoenix. They could have made a decision that endangered Harry's life without his knowledge. Feeling used and discarded, Harry runs away. Voldemort, through his Death Eaters, finds Harry and manipulates him. He tells Harry that he can give him a place where he will be respected and not betrayed again. Harry, still young and naive in some ways, falls for Voldemort's lies and joins him, leading to a very different kind of war in the wizarding world.
One possibility could be that she begs for the truth. In a lot of fanfics, when Hermione is betrayed, she might beg the person who betrayed her, perhaps Harry if the plot is set that way, to tell her why they did it. She's a character who values loyalty and knowledge, so being betrayed would be a huge shock. And her begging could be a way to try and make sense of the situation, to get back to the stability she once knew.
One common theme is healing. Harry has been through a lot during the war, so in these fanfics, he often has to deal with his emotional and physical scars. Another theme is rebuilding. The wizarding world is usually in shambles after the war, and Harry is involved in putting it back together.
Well, it could be that in the fanfic, Harry realizes the full extent of the destruction the war has caused not just to people but also to the wizarding world as a whole. He might cry for the broken relationships, the damaged places, and the future that seems so uncertain now. All the trauma and stress that he bottled up during the war comes pouring out in tears.
One possible plot could be that Harry and Hermione travel the wizarding world together, documenting all the post - war changes. They might visit Hogwarts, which is being rebuilt, and help in the restoration process, reminiscing about their old school days as they do so.