No. Abuse is never an appropriate topic, especially when it involves beloved characters from a popular series like Dragon Ball. It goes against the positive values that the series usually promotes.
Fanfictions can vary widely in their themes and content. In the case of 'yamcha abuses bulma fanfiction', it's a rather disturbing concept considering the characters. In the original Dragon Ball series, Yamcha and Bulma have a past relationship that was not like this at all. So this fanfiction might be an attempt by some writer to explore extreme and negative situations, but it's not something that would be considered positive or in - keeping with the general feel of the Dragon Ball franchise.
In these fanfics, a major theme is the power of memory. Bulma's amnesia makes Yamcha realize how much their shared memories mean. There's also the theme of adaptability. Yamcha has to adapt to a Bulma who doesn't remember him or their past. This can lead to some interesting character development. Another theme could be the exploration of the past. As Yamcha tries to help Bulma remember, they both end up exploring their past relationship in a new light. This can bring out hidden emotions and secrets that were previously overlooked.
Well, it could be about Yamcha making Bulma cry perhaps because he said something really mean. Maybe he criticized her for being too obsessed with her inventions and not paying enough attention to their relationship.
By showing their shared history. Flashbacks to their early days together can add depth. For example, remember when they first met? That could be a great starting point to build on their relationship in the fanfic.
Perhaps a fanfic could be about an alternate universe where Yamcha was always more confident in his relationship with Bulma. In this universe, they go on adventures together, exploring new planets and having to rely on each other. This would strengthen their bond and make for an exciting story about their relationship.
There are quite a few fanfics out there. 'Yamcha's Struggle with Bulma's Amnesia' is a fanfic that focuses on Yamcha's emotional turmoil as he tries to help Bulma regain her memories. Some fanfics might also include other elements from the Dragon Ball universe, like the Saiyans, while still centering around this trio. It's all about how the authors choose to play with the idea of amnesia in relation to these characters.
For Yamcha, you can focus on his growth from being a bit of a comical character to a more serious and respected fighter in the context of his relationship with Frieza. Maybe he learns from Frieza's cold and calculating nature how to better strategize in battles. For Frieza, his development could be about him learning to care for someone other than himself. He could start to see Yamcha as an equal, which is a huge shift from his usual superiority complex.
Yes, there are likely fanfictions with such a plot. Fanfiction writers often explore alternative relationship dynamics in the Harry Potter universe. However, this goes against the canon where Harry ends up with Ginny.