A plotline could involve Broly being sent to Kale's universe by some sort of interdimensional rift. Kale initially sees him as a threat and attacks. But as the fight progresses, they start to understand each other's power and motives. Or perhaps a fanfic could have a story where both Broly and Kale are training on the same planet. Their training methods clash, leading to a fight where they both learn from each other and grow stronger in the process.
A plotline could start with Frieza hearing about Broly's power and being jealous. He then devises a plan to ambush Broly. But Broly, being extremely perceptive in his own way, senses Frieza's approach and is ready for the fight. As the fight progresses, Frieza realizes that Broly is much stronger than he expected and has to use all his dirty tricks to try and win. Or perhaps the plotline could involve Broly being captured by Frieza's forces, and then Broly breaks free and goes on a rampage against Frieza and his minions.
One interesting concept could be the power struggle. Beerus is an extremely powerful deity in the Dragon Ball universe with god - like powers, while Naruto has his own set of formidable ninja abilities. In fanfiction, they might explore how Naruto's chakra and jutsu would fare against Beerus' energy blasts and hakai ability. Another concept could be the clash of their worlds. The ninja world of Naruto is very different from the Dragon Ball universe, so seeing how the two settings interact, like how Naruto's friends and village would react to Beerus' presence, can be really engaging.
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.
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.