It's fictional in the sense that the series doesn't really portray it like that. Vegeta has his own personality and pride. He may be influenced by Bulma in different ways, but not in a way that implies he can't resist her'seductions'. Their relationship is more about two individuals from different backgrounds coming together, learning from each other, and growing in love and respect over time. For example, Vegeta became more in - touch with his emotions because of Bulma, not because of some sort of seductive power she has over him.
It probably started from the contrast between Vegeta's tough and stoic Saiyan nature and Bulma's more outspoken and flirty personality. Fans might have thought that her boldness could be something that Vegeta, who is not used to such behavior, would find hard to resist. But this is all speculation and part of the creative interpretations in the fan community.
I don't think it's accurate to say that Vegeta can't resist Bulma's seduction. Vegeta is initially a rather cold and battle - focused character. His relationship with Bulma developed gradually over time. It was more about them growing closer through shared experiences, like raising Trunks, and facing various threats together. Seduction doesn't really seem to be in line with the nature of their relationship.
In the fanfiction, their relationship is full of passion. It's not just a physical passion but also an emotional one. Vegeta, who was once a cold - hearted Saiyan, has softened because of Bulma. He shows his love in his own way, like training hard to protect her. Bulma, in turn, is attracted to Vegeta's strength and his gradual transformation into a more caring person. They bicker sometimes, like any couple, but it's all part of their unique dynamic.
Vegeta would likely still be his proud and strong - willed self, but with a newfound tenderness towards Bulma. He might be a bit more protective and less quick to anger. Bulma, on the other hand, would be her intelligent and sassy self, always ready to challenge Vegeta in a playful way.
The story of Vegeta and Bulma in 'life happens vegeta and bulma story' is full of character development. Vegeta, the once cold - hearted Saiyan, started to change because of Bulma. He became more involved in family life. Bulma, on the other hand, had to deal with Vegeta's Saiyan pride and his constant pursuit of power. Their love story is not a typical one. It's about two very different individuals coming together. Their son Trunks is a symbol of their union. And through all the trials and tribulations in the Dragon Ball world, they managed to stay together and support each other in their own ways.
Maybe Bulma is too busy with her scientific research and family matters to be interested in fanfic about Vegeta. She has a lot on her plate, from taking care of Trunks to working on new inventions.
Often, Vegeta becomes more in touch with his emotions. He starts to care about things other than just fighting, like his family with Bulma. He may show more love and protectiveness towards her and their child.
There are many great fanfictions that focus on their relationship in a more family - oriented way. For example, some stories might explore how they raise Trunks together, showing their growth as parents and partners. Others could be about the early days of their relationship, like how Vegeta first started to open up to Bulma and how she saw through his tough exterior.
Maybe in the fanfic, Vegeta did something unforgivable like betraying Bulma's trust or putting her in great danger while under the influence of the Majin transformation. For example, if he endangered their family or made a pact with the enemy that directly opposed Bulma's values.