One common theme is justice. Since Harry is angry, it often involves him seeking justice for wrongs done to him or his friends. For example, if a character was wrongly accused in Hogwarts, Harry's anger would drive him to clear their name.
The fanfic could start with Harry being called to trial for something like using underage magic, which he didn't actually do. He is angry because he has been through so much already, fighting Voldemort and his Death Eaters, and now he has to face this unjust trial. His anger could fuel him to find evidence on his own to prove his innocence. He might start investigating who really cast the magic in question, leading him on a new adventure while still in the middle of the trial drama.
One 'angry Harry Potter fanfic' could be those where Harry gets really mad about the unfair treatment he receives at the Dursleys' in some fan - created scenarios. For example, a fic might show him lashing out in a more extreme way than in the original books when Dudley bullies him again.
In some fanfictions, Harry Potter might be angry at the Order because he feels they are keeping secrets from him. He is used to being in the thick of things and when the Order withholds information, it can make him feel left out and untrusted.
One common theme is betrayal. Harry often feels betrayed by those he trusts, like the Ministry of Magic or certain teachers, and his anger stems from that. For example, in some fanfics, he discovers that they have been using him for their own purposes.
There's no way for me to know for sure who the creator of 'angry harry and the seven fanfic' is. Fanfics are often created by passionate fans anonymously or under a pen name. It could be someone in a small fan community or just a lone writer who wanted to explore their own ideas about this 'angry harry' concept and the seven elements in the story.
Well, 'angry harry and the seven fanfic' could potentially be a story where 'angry harry' is the main character. The'seven' might refer to seven tasks, seven friends, or seven challenges he has to face. Fanfic usually means it's a work created by fans, so it's likely a creative take on an existing story or character, but without reading it, it's hard to say more precisely.
Perhaps a fanfiction where Harry is angry due to the danger the Goblet of Fire has put his friends in. He realizes that just by being a part of the Triwizard Tournament, his enemies might target his friends to get to him. His anger could drive him to take extra precautions to protect them, and also make him more determined to succeed in the tournament so that he can prove that he's not a coward and that he can handle whatever comes his way.
A lot of fanfictions that are angry could be centered around Snape. There are fans who are either very angry at Snape for his actions towards Harry and his friends, or angry on his behalf because they feel he was misjudged. So, you might find angry fanfictions that either demonize him further or try to redeem him more forcefully than in the original story, showing the author's strong emotions regarding this character.
You can start by looking on popular fanfiction websites such as Fanfiction.net or Archive of Our Own (AO3). These platforms have a wide variety of fanfictions, and you can use their search functions to specifically look for 'angry harry potter' fanfiction. Just type in the relevant keywords and browse through the results.