In a story where Harry is raised by a boggart, he could have a very distorted view of the world. The boggart, not being a normal caregiver, might not be able to provide the love and stability that a normal family would. So, Harry might be more withdrawn and distrustful. He might also have a hard time making friends at Hogwarts as his upbringing by a boggart could have made him seem strange to other students.
His magic might be different. Since he was raised by a boggart, he could have developed some unique ways of using magic related to fear or illusions. For instance, he might be able to sense when someone is about to be afraid and use that to his advantage in a duel. Also, his personality could be more solitary as he might not have had the normal social interactions growing up. He'd be more used to dealing with his own fears alone rather than sharing with others like a normal child would.
One possible scenario in this fanfiction could be that Harry Potter and Sasuke are somehow transported to a shared magical realm. When they encounter a Boggart, Harry might see Voldemort at first, given his past traumas. Sasuke, on the other hand, could see Itachi. But as they realize they are in this together, they combine their magical and ninja skills to defeat the Boggart. Maybe Harry uses a Patronus charm while Sasuke uses his Sharingan to disorient the Boggart.
A common boggart scenario in fanfiction is related to the characters' insecurities. For Harry, it could be that the boggart shows him as the cause of all his friends' misfortunes, emphasizing his fear of being a burden or a danger to those he loves. This can add more depth to his character and explore his self - doubts further.
Perhaps in the fanfiction, there is a magical tournament where both Harry and Sasuke are participants. One of the challenges involves facing a Boggart. Harry's fear of losing his wand (which is like his life in the wizarding world) and Sasuke's fear of losing his eyesight (since his Sharingan is so crucial) are what the Boggart targets. They initially struggle as they are used to fighting their battles alone. But as the Boggart gets stronger, they realize they need to work together. Harry uses spells to distract the Boggart while Sasuke uses his ninja speed to get behind it and deliver a final blow.
One interesting 'Harry Potter Boggart' fanfiction could be one where Neville's boggart turns into something unexpected, like a happy Snape instead of his usual grandmother. It adds a unique twist to the character's fear and development.
Some 'Harry Potter Boggart' fanfics focus on how different Hogwarts houses might face boggarts. In Gryffindor, a common boggart could be seen as cowardice, but in one fanfic, a Gryffindor's boggart is actually the harm coming to their friends because they value friendship so much more than their own bravery.
Harry could use his love for his friends and family. The power of love has been shown to be strong against Voldemort in the original series. So, when facing the Boggart - Voldemort, he could focus on the love he has for Hermione, Ron, and the rest of his friends, and this positive emotion could transform the Boggart into something less terrifying.
In many Harry Potter fanfictions, the concept of being 'raised by darkness' can take various forms. It might involve a character being brought up in an environment influenced by dark magic or dark wizards. For example, a character could be raised in a family that secretly practices the Dark Arts. This could lead to the character having a different moral compass compared to those raised in the light. They may struggle with the line between right and wrong, as their upbringing has exposed them to unethical magical practices.