One reason could be betrayal. If someone he trusted, like a fellow ninja or an old acquaintance, turned out to be working for his enemies, that would surely make him pissed. It's a huge blow to his trust, which is a big part of his character.
In the fanfic, Naruto might also get pissed if his ideals were being mocked or undermined. He has always strived for peace and acceptance in the ninja world. If someone were to say that his dreams were naive or impossible, it would definitely piss him off as he's put so much effort and heart into his beliefs.
Another factor could be the threat to his loved ones. Naruto is extremely protective of his friends and family. So, if an enemy were to target them directly, it would send him into a rage. He'd be pissed off at the audacity of the enemy to go after those he holds dear.
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.
Well, in a 'naruto gets pissed fanfic', Naruto might get angry over various things. It could be because of an enemy taunting him about his past, like how he was an outcast in the village as a child. He could also get pissed if his friends were in danger and he felt powerless to help them right away.
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.
Sasuke could make Naruto pissed off if he goes back to his old ways of seeking power and revenge. Naruto has worked hard to bring Sasuke back to the right path, and if Sasuke strays again, it would surely anger Naruto.
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.
In a 'naruto gets pissed off fanfic', one possible scenario could be that Naruto discovers someone has been slandering his friends behind their backs. He would get pissed off and confront the person directly, his eyes blazing with anger.
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.
Maybe he'll go on a rampage in the fanfiction world. He could start using his powerful jutsu to show his anger, like unleashing a Rasengan on the source of his annoyance.
Maybe Naruto gets pissed off because his friends don't believe in him. For example, if they suspect him of being involved in something bad without evidence.
First, the author should stay true to Naruto's character. By studying his traits like his determination, his loyalty to his friends, and his never - give - up attitude in the original anime. For example, don't make him a coward when he's known for being brave. Second, improve the plot. Make it more logical and in line with the Naruto world. No sudden, out - of - the - blue events that don't fit. Third, work on the writing quality. Use proper grammar and spelling so that readers can easily follow Naruto's journey in the fanfic.