One common theme is isolation. When Harry loses everything, he often finds himself alone, cut off from the friends and the world he once knew. Another theme is despair. Losing everything makes him question his existence and purpose. For example, in many such fics, he might wonder why he should keep fighting when he has lost so much.
Well, in the 'harry loses everything fanfiction' like 'Harry's Shattered Existence', he loses his mentors one by one. Dumbledore is killed in a different way and Sirius never gets a chance to be there for him. Also, 'Desolate Harry' is a fic where he loses his sense of purpose. He is left with nothing but his own doubts and the ruins of what could have been a great life.
There might be a new dark wizard or witch that we don't know in the main series. This new character could be extremely powerful and target Harry specifically. They might have a vendetta against Harry's family or just want to take over the wizarding world by first destroying Harry, who is seen as a symbol of hope, and thus make him lose everything.
In this kind of fanfiction, Goku might lose his family. For example, his friends and loved ones could be killed by a powerful new enemy. This would leave him in a state of deep despair and loneliness, and he would have to find a way to carry on without them.
It could be Voldemort. Voldemort might use Harry's love as a weapon against him. He could either kill her or turn her against Harry. Another possibility is Draco Malfoy. Maybe Draco tricks Harry's love into thinking he's a better choice. Or it could be a new, unknown dark wizard who targets Harry through his love.
It could be about a fan - created story where the character Harry has ownership over everything. Maybe it's in a fictional world where he has amassed great wealth, power, or all sorts of possessions.
In the fanfiction, it could be related to his relationship with Ginny or other important people in his life. If Ginny left him for some reason, like being under a spell or falling in love with someone else because of some magical interference. Harry, who has always been through so much, might see this as the final straw. His heartbreak, combined with all the past burdens, could make him lose the will to live. He might feel like there's nothing left for him in a world where he can't even have a happy relationship with the person he loves.
Well, one possibility is that it could be about Harry's struggle to adapt to his new disability. Maybe he has to learn new magic or spells to help him move around. For example, he might discover a spell that creates a temporary prosthetic leg. Another idea could be that his friends rally around him, with Hermione researching ways to heal his leg completely and Ron being his emotional support. It could also show how he overcomes the challenges in his daily life at Hogwarts, like climbing the stairs or participating in Quidditch in a different way.