Majin Buu was created by the wizard Bibidi. Bibidi was an evil being who made Majin Buu as a weapon of destruction. Majin Buu was originally a pure and innocent being, but Bibidi's evil influence turned him into a rampaging monster.
One possible fanfiction could involve Naruto being transported to the Dragon Ball universe where he meets Female Majin Buu. Maybe they start as adversaries at first. Naruto, with his ninja skills, tries to fight her. But then they realize they have some common ground in their love for food. And they could end up teaming up against a greater threat in the Dragon Ball world.
One common theme could be redemption. Just like the original Majin Buu, a female version might go through a journey of changing from a more menacing or chaotic being to a more benevolent one. Another theme could be friendship, perhaps forming unexpected alliances with other Dragon Ball characters.
The plot could start with Majin Vegeta's pride getting in the way. He might feel that Bulma is disrespecting his new power as Majin Vegeta. So, he challenges her to a fight. Bulma initially panics but then decides to stand her ground. She uses her knowledge of Saiyan physiology (from all the time she's spent with Vegeta and the other Saiyans) to find his weak points. However, she also tries to reach out to the real Vegeta inside. As the fight progresses, Vegeta starts to see how strong - willed Bulma is and slowly begins to break free from the Majin influence.
Well, it could be about Naruto having the unique powers of Majin Buu. Maybe he'd have the ability to regenerate like Buu. And his personality might change a bit, being more unpredictable. He could use Buu's techniques in battles against his enemies in the Naruto world.
In a fanfiction where Naruto fuses with Majin Buu, there could be some really wild power combinations. Naruto's chakra and Buu's unique abilities like regeneration and absorption might create a super - powerful being. For example, Naruto could potentially use his Rasengan with Buu's stretchy body to create new and unpredictable attacks.
I'm not sure about specific 'female majin buu fanfic' offhand. You could try searching on fanfiction websites like Archive of Our Own or FanFiction.net. They usually have a wide variety of fan - created works related to different characters, including Majin Buu.
Another concept could be that a part of Majin Buu's essence gets mixed with Naruto's chakra during an experiment gone wrong. Naruto now has to control this new power within him while also keeping his own identity, all the while dealing with the suspicion of his friends and the potential danger it poses to the village.
Majin Buu could be a chaotic antagonist. His unpredictable nature and immense power would make him a formidable foe for Naruto and his friends. He might start randomly causing destruction in the ninja world, and the characters would have to find a way to stop him.