To find out the author of the 'harry gets pissed fanfiction', you could try searching on fanfiction platforms. Look for the story and check the details page. Usually, the author's name or username will be clearly stated there.
The 'harry gets pissed fanfiction' might center around Harry experiencing a range of emotions that lead to him being pissed. It could be due to a betrayal, like if someone he trusted in the fan - created story did something against him. It might also be related to his goals being thwarted, for example, if he was trying to achieve something important and someone or something got in his way.
Sasuke could be a possible cause. If Sasuke were to go back on his word about protecting the village or if he were to harm their friends again, Naruto would be pissed. Their relationship is complex, and Sasuke's actions often have a strong impact on Naruto.
A sense of powerlessness can also be a theme. When he's faced with situations where he can't immediately solve a problem or protect those he cares about, Harry might get pissed off. This often leads to him finding new ways to gain power or take control in the fanfiction.
Percy is surely a main character in this fanfiction. Depending on the universe it's set in, if it's related to a series like Percy Jackson, characters such as Annabeth, Grover, or his other demigod friends might also be important characters. They could either be the cause of Percy's anger or the ones who try to calm him down and help him through his angry state.
I don't have information about the author of this particular fanfiction. There are so many fanfiction writers out there, and without more context or research, it's impossible to say who created it.
Another good one is 'When Harry's Temper Flared'. Here, it starts with a small incident in the Gryffindor common room that snowballs into a major event where Harry gets extremely pissed off. The writer focuses on Harry's relationships with his friends during this time of anger and how they react to his outbursts.
Sasuke could be the cause. If Sasuke were to betray Naruto again in the fanfiction, it would surely make Naruto pissed off. Their relationship is complex and Sasuke's actions have a big impact on Naruto.
Well, 'percy gets pissed' in a fanfiction could potentially explore Percy's character in a different light. Maybe he's been wronged in some way in the fan - created universe, like betrayed by a friend or faced with a difficult situation that makes him lose his temper. It could then lead to all sorts of plot developments, such as him seeking revenge or trying to overcome his anger in a journey of self - discovery.
One scenario could be when Naruto finds out that someone has been spreading false rumors about his friends. This would surely make him pissed as he values his friends deeply.
A new, powerful and arrogant villain introduced in the fanfic could be the cause. This villain could constantly mock Naruto and his ideals, and try to undermine his efforts to protect the village. Such blatant disrespect would make Naruto really pissed off as he is very protective of his home and the values he stands for.