One way could be for Naruto to use his Sage Mode combined with the power of all the tailed beasts. This super - powered form might be able to match Majin Boo's strength. Also, Sasuke with his Rinnegan could try to use some space - time ninjutsu to trap Majin Boo. And the rest of the shinobi could support them with their various jutsus. For example, the Nara clan's shadow techniques could be used to hold Majin Boo in place while Naruto and Sasuke attack.
In a fanfiction where Majin Boo invades the Naruto universe, the first thing that might happen is that there would be mass panic. Majin Boo's appearance would be something out of the ordinary for the Naruto characters. The Kages would have to quickly assemble and come up with a plan. They might try to use sealing jutsus which are common in the Naruto world. However, Majin Boo's resistance to such things in his own universe might make it difficult. The characters like Rock Lee, who rely on physical combat, would find it tough as Majin Boo can take a lot of punishment. And the story could also explore how the different chakra natures interact with Majin Boo's magic - like powers.
They could use teamwork. Naruto with his powerful jutsu like the Rasengan, and Sasuke with his Sharingan and Chidori could combine their attacks. Their other friends can also support them. For example, Rock Lee could use his taijutsu to distract Frieza while Naruto and Sasuke prepare a big attack.
A really scary scenario could be that Alana (Honey Boo Boo) is in an old attic with just her flashlight. She hears strange scratching noises coming from the walls. When she shines the flashlight on the wall, she sees a huge, hairy spider as big as her head. But as she tries to move away, the flashlight reveals that the whole attic is filled with spiders of all sizes. They start to crawl towards her, and she can't find a way out because the door has mysteriously locked. She's trapped with only the flashlight, which is about to die out.
One possible plot could be that Majin Boo has done something really bad that affects Bulma. But then, through a series of events, like Majin Boo saving Bulma's life or showing remorse in a very genuine way, Bulma begins to consider forgiveness. Maybe Majin Boo has to sacrifice something important to prove his change of heart, and in the end, Bulma fully forgives him.
Naruto himself is often a central and popular character. Since it's a Naruto - related fanfiction, his presence is expected. Sasuke is also likely to be popular as he is one of the main characters in the original Naruto series. And any new majin - created characters can also gain popularity if they have interesting backstories and powers.
It could also be due to the general nature of Majin Boo. He was initially a villain created for evil purposes. His appearance and the way he carried out his actions were often grotesque and malevolent. Bulma, who is used to a more civilized and scientific environment, might be repulsed by his very existence and find it unforgivable that he was able to cause so much trouble in their world.
In a fanfiction, the characters in Naruto could interact with King Boo in a more diplomatic way. Maybe they find out that King Boo has some valuable information about an upcoming threat to the ninja world. So, they offer King Boo a deal - if he shares the information, they will help him with something he desires, like finding a way back to his own dimension.
The Naruto characters could try to find Frieza's weaknesses. Maybe his overconfidence could be exploited. They should start by observing how he fights. If they notice that he has a pattern in his attacks, they can use that against him. Rock Lee could use his Taijutsu skills to quickly move around Frieza and try to find an opening. Ino could use her mind - transfer jutsu to try and disrupt Frieza's thoughts if possible. Also, the ninja could use the terrain of the Naruto universe to their advantage. Hide in the forests or mountains and launch surprise attacks on Frieza instead of facing him head - on all the time.
Obviously, Naruto would be one of the main characters. His never - give - up attitude and powerful chakra would be crucial in fighting the aliens. Sasuke would also be important, with his Sharingan and combat skills. Sakura, with her medical ninjutsu, could play a big role in treating the injured ninjas during the invasion. Kakashi could lead the strategic planning, using his vast experience.
If Naruto fused with Majin Buu in fanfiction, the story might start with the fusion's initial confusion about its new powers and identity. As it tries to figure things out, it could attract the attention of various villains who see it as a threat or an opportunity. The story could then be about the fusion's journey to master its powers and find its place in the world while dealing with these antagonists.