The loss of many friends and loved ones is a major cause. People like Fred Weasley, Lupin, and Tonks. Their deaths weigh heavily on Harry's heart. He feels guilty that he couldn't save them all, especially Fred who died in the middle of the battle.
Often, he'll start to heal by reconnecting with nature. Maybe he takes long walks in the Forbidden Forest. It gives him a sense of peace away from the chaos that the wizarding world has become post - war. The quiet and the beauty of the forest start to soothe his troubled mind.
Common causes of depression in children include biological factors. Sometimes hormonal imbalances or chemical changes in the brain can occur for no obvious external reason and contribute to depression. Traumatic events like abuse, whether it's physical, emotional or sexual, are also major causes. A child who has gone through such a horrible experience may struggle with feelings of worthlessness and hopelessness, which are key symptoms of depression.
Another cause could be the pressure she feels to be a symbol of the rebellion. In fanfics, she might feel trapped by this role. She has to constantly uphold an image for the people, but inside she is just a broken girl. This disconnect between her public self and her true self can cause a great deal of inner conflict and ultimately depression.
One possible cause could be the loss of a loved one. In many stories, this kind of trauma can lead to depression. Percy might be struggling to come to terms with the death or departure of someone close to him.
In these fanfictions, the theme of loss is prevalent. Harry has lost his former self, his full capabilities, and he mourns that. Redemption is also a theme sometimes. He tries to redeem himself in his own eyes, feeling like he's less of a hero because of his disability. And there's the theme of discovery, as he discovers new parts of himself and new relationships that he might not have otherwise.
One common theme is the struggle of Harry to adapt to his new situation. After the war, he already has a lot to deal with, and the added aspect of mpreg brings more challenges.
One common theme is isolation. Characters often feel alone in their struggles, just like in the real world. Another is the struggle with self - worth. For example, they might feel they are not good enough in the wizarding world. And loss is also a big theme, like losing a loved one or a sense of purpose.
In a fanfic, one possible cause could be the loss of his loved ones. If he were to lose Sasuke again, this time perhaps permanently, it could send him into a deep depression. He's always been so focused on bringing Sasuke back, and if that hope is completely dashed, it would be a huge blow.
Rebuilding. After the war, not only do they rebuild their relationship, but often in these stories, they are also involved in rebuilding the wizarding world. Like helping to repair Hogwarts or restoring the trust among the wizarding community.
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.