One possible fanfiction could be where Goku is faced with an otherworldly entity that he can't sense or understand. This makes him scared as his usual confidence in his power is shaken. Maybe it's a being from a different dimension that defies all the rules he knows about fighting.
One reason could be the popularity of both characters. Writers want to combine two well - loved anime heroes. Another reason might be the similarity in their underdog - turned - hero stories. Naruto was an outcast in his village at first, and Goku was a low - class Saiyan. So, by making Naruto Goku's reincarnation, it gives a new twist to Naruto's character development.
Well, without actually reading the 'dumb dumb boys short story', it's hard to say precisely. But generally, if it's about dumb boys, it could explore themes like misunderstandings. For example, their actions might be misinterpreted by others because they don't communicate or act in the 'normal' way. It could also be a comical story where their 'dumb' actions lead to funny situations.
You can focus on their emotional bond. For example, show how Goku's pride in Gohan's growth and achievements affects their relationship. It could be about Gohan seeking Goku's approval and Goku being there to give it wholeheartedly.
One common scenario is when new and powerful enemies emerge. Goku will immediately position himself between Gohan and the threat. He'll use his body as a shield if necessary. Another scenario is when Gohan is training and pushes himself too hard. Goku steps in to make sure he doesn't overexert and get injured. In some fanfictions, when Gohan is exploring new places, Goku follows closely behind to protect him from any unknown dangers.
I haven't come across such a fanfiction specifically. It seems like a very strange and unlikely crossover considering they are from different fictional universes. Erza Scarlet is from 'Fairy Tail' and Goku is from 'Dragon Ball'. The two universes have very different rules, powers, and storylines, so this would be a really out - there concept for a fanfiction.
Well, Vegeta would be a likely character. He might be initially suspicious of the female Goku. Maybe he thinks she's a threat or just can't believe there's another Goku - like being. He could be there to add some comical moments as he tries to understand the situation.
One possible reason could be some sort of magical or energy - based interference. Maybe an enemy has cast a spell that locks his form. Another reason might be that his body has reached its limit in terms of evolution for the time being, and it needs some special trigger to break free from being stuck.
In this fanfiction, it could be really exciting. Naruto's transformation into a godlike being would be gradual. Goku could introduce Naruto to the concept of different levels of power, like Super Saiyan levels. Naruto might then develop his own 'god - like' forms based on his Uzumaki heritage and the new knowledge from Goku. His relationships with his friends in Konoha might also change as he becomes more powerful. He could become a more confident leader and protector, and his story would take on a whole new dimension of adventure and power - seeking.