Beerus would probably win. He has the status of a God of Destruction, which means he has a certain level of power and abilities that are unique. His Hakai ability can erase things from existence. Broly is strong, no doubt, but he is still a mortal (in a sense). Beerus has been shown to be far above most mortals in terms of combat ability and raw power. In a fanfic, unless the writer completely changes the power dynamics, Beerus has the edge.
In fanfiction, it's really hard to say for sure. Different fanfictions might have different outcomes. Some might make Goku Black super powerful and give him the win, while others would keep Beerus as the dominant force due to his status as a God of Destruction.
Beerus would probably win. He is a god of destruction in the Dragon Ball universe. His power levels are off the charts compared to Naruto. He can destroy planets with a snap of his fingers, and his combat skills are far beyond what Naruto has been shown to be capable of in the Naruto universe.
One scenario could be that Goku surprises Beerus with his speed and initial attacks as SSJ4. But then Beerus counters with his hakai and forces Goku to dodge constantly. Another could be that Beerus underestimates Goku at first and Goku manages to land some powerful blows.
Well, in many fanfictions, SSJ4 Goku is often depicted as having a chance against Beerus. SSJ4 Goku has shown incredible strength and combat skills. But Beerus has the power of a God of Destruction. His hakai ability could potentially wipe Goku out. Still, if the fanfiction is written in a way that gives Goku some new power - up or a special advantage, he could win. It really depends on the creative direction of the fanfic writer.
I'm not entirely sure specifically what a 'beerus raps beerus fanfic' is about without more context. It could potentially be a fan - created story where the character Beerus is rapping. Maybe it involves Beerus expressing his thoughts, his powers, or his experiences in the form of rap within the context of a fan - made fictional narrative.
You could try looking on fan - fiction websites like Archive of Our Own or FanFiction.net. They usually have a wide variety of fan - created works, and there's a good chance you might find a 'beerus raps beerus fanfic' there.
Beerus would likely be more powerful. He is a god of destruction in his own universe with incredible cosmic powers. Naruto is extremely powerful in his world, but his power is mostly based on chakra and ninjutsu, which is on a much smaller scale compared to Beerus' ability to destroy planets with a flick of his finger.
Well, Naruto could be in awe of Beerus' power. Maybe he tries to learn some of Beerus' combat techniques. Since Naruto is known for his determination, he might pester Beerus to train him.
With King Kai, Beerus as a girl could have a different kind of relationship. She might be more patient with him. King Kai might be a bit more nervous around her at first, but then they could develop a more comical and friendly rapport, with Beerus teasing him in a more light - hearted way.