One common theme could be Naruto's internal struggle with his rage. Maybe he's constantly fighting against the darkness within himself that the rage represents. Another theme might be how his relationships are affected by his rage, like with his friends or sensei.
In 'Naruto is full of rage fanfiction', a prevalent theme could be the transformation of Naruto due to his rage. He might develop new powers or abilities as a result of his intense emotions. Also, the way the village reacts to a rage - filled Naruto can be a theme, whether they fear him or try to help him overcome his anger.
Well, often in such fanfiction, the exploration of Naruto's past traumas that fuel his rage is a theme. For example, his lonely childhood as an outcast in the village. His rage could also lead to him going on a journey of self - discovery to find ways to control it, which can be another theme.