Well, the plot could involve them fusing due to some kind of magical or technological accident. Maybe they are trying to defeat a powerful enemy together and their combined energy causes them to fuse. They could then have a new form with combined powers and a unique personality that is a blend of their own.
Their fusion could change the power dynamics. Since both Bulma and Chichi are important figures in the Dragon Ball universe, their fusion would create a new and unexpected force. Enemies might be caught off - guard by this new entity. It could also inspire new alliances as other characters see the potential of fusing.
One common theme is friendship. Since they are both important female characters in the Dragon Ball universe, fanfics often explore how they become friends and support each other. For example, they might team up to deal with some threats in the story.
Well, if they fuse, the new character would likely have Bulma's inquisitive nature. They would be constantly curious about new things, especially in the realm of science and technology. At the same time, they would also possess Chichi's determination. So when facing challenges, they would be very persistent.
In a fanfic, the Bulma - Chichi fusion could be part of a tournament arc. They enter the tournament fused and shock everyone with their abilities. Their opponents underestimate them at first, thinking it's some kind of strange trick. But as the battles progress, they show that their fusion is not only powerful but also has a deep understanding of both martial arts and strategic thinking.
One possible plot could be that Bulma and Chichi team up for a scientific - martial arts tournament. Bulma uses her intelligence to create unique gadgets for Chichi to use in the combat part of the tournament. This brings them closer as they train together and face various opponents.
Trunks could be an interesting fusion partner for his own mother. This would create a really complex character. They share a lot of knowledge about the future already. Fusing could enhance their ability to prevent disasters in the future timeline even more, perhaps by creating a time - shield that can protect the future from any time - traveling villains.
It could also be due to the way the fanfic writers handle their characters. If they write Bulma as a prideful character and Chichi as someone who challenges that pride, either directly or indirectly, Bulma might be written as hating Chichi. Fanfic often takes creative liberties and this could be one of the results.
It could be Frieza. He might be interested in Bulma's technology for his own evil purposes and sees Chichi as a threat because of her connection to the powerful Z - Fighters. So he tries to stop their partnership and steal Bulma's inventions.
One idea could be that Bulma discovers a new technology that allows her to fuse with different characters' minds, not just their bodies in a traditional sense. She could fuse with Goku to understand his pure love for fighting and gain some of his combat instincts.