One possible theme could be self - discovery. When Harry is alone and angry all summer, he might start to explore his own identity and what really matters to him.
Finding specific 'Angry Harry Alone All Summer' fanfiction can be a bit of a hunt. Some fanfictions might focus on Harry's emotional state during a particular summer when he's angry and alone. It could be a story exploring his inner turmoil, his growth, or his relationships during that time. However, without more context about the origin of this concept (is it a very niche idea within a big fandom or something unique?), it's difficult to point directly to a particular piece of fanfiction. But as I said before, exploring large fanfiction repositories is your best bet.
One reason could be that it adds an extra layer of drama to the story. Harry's character has always had a bit of a lonely streak in the original series, and fanfiction writers like to explore that further. For example, it gives them more room to develop his character in new and different ways.
One popular 'Harry is all alone' fanfiction could be 'Alone in the Shadows'. It delves deep into Harry's emotions as he faces solitude. Another might be 'Isolated Harry' which shows his journey of self - discovery while being alone. And 'Harry's Solitary Path' is also quite good, exploring how he copes with the lack of support around him.
Loneliness and isolation are big themes. These fanfics often explore how Harry feels being alone, the emotional turmoil he goes through. Also, the theme of inner strength is present. Harry has to dig deep within himself to find the strength to face whatever comes his way while alone.
It's popular because it shows a different side of Naruto. We usually see him with his friends, but when he's all alone, it creates a sense of vulnerability that's really interesting to explore.
Hermione could still be a common character. Even in fanfiction where Harry is alone, Hermione might be mentioned in his thoughts or in flashbacks as someone who has influenced him. For example, he might recall her advice on how to study magic when he is facing a difficult spell alone.
Well, in some cases, there could be minor characters from the original series who still interact with Harry on a limited basis. For example, Neville Longbottom might make an appearance. Even though Harry is alone for the most part, Neville could cross paths with him and have a brief conversation or exchange that has an impact on Harry's journey.
Hermione could be one of the characters to help Harry. She's intelligent and resourceful, so she could provide practical help like finding a good doctor or helping with magic - related pregnancy issues if it's in a magical world. Another could be Hagrid. He has a big heart and could offer emotional support and perhaps a place for Harry to stay if he needs it.
One interesting aspect could be Harry's self - discovery journey. In many 'harry is alone fanfiction' stories, he has to rely solely on himself, which forces him to dig deep into his own capabilities. For example, he might learn new spells on his own, without the help of his friends or teachers. This makes for a very different Harry than the one in the original series.