Adventure is another typical theme. They could go on adventures together, either in the Other World or on Earth. These adventures can range from fighting new villains to exploring uncharted territories. This theme allows for a lot of action and excitement in the fanfictions.
One could expect an exciting adventure. Maybe it'll involve Goku's power being used in a unique way to protect the timeline that Supreme Kai of Time oversees. It could also show a different side of their relationship, perhaps a friendship that develops as they face challenges together.
In the Dragon Ball universe, there are many strange and wonderful things. King Kai might have access to some rare or magical items. He could use one of these items to help Goku's tail grow back. For example, there could be a special fruit on his planet that has regenerative properties. When Goku consumes it or King Kai uses it in some other way, it triggers the growth of the tail.
One possible storyline could be that Goku is accidentally transported to Alucard's world. They start off as enemies but then gradually learn about each other's powers and come to respect one another. Another could be that a powerful villain manipulates them into fighting each other. In this case, they might realize they are being used and team up against the real enemy.
It's really hard to say. Goku is extremely powerful with his Super Saiyan forms and incredible combat skills. But Alucard has his vampiric powers like immortality and the ability to control shadows. In a fanfic, it could go either way depending on how the author wants to write it. Maybe if the author wants to emphasize speed, Goku might have an edge. But if it's about dark, mysterious powers, Alucard could come out on top.
Another storyline could involve Supreme Kai of Time getting into trouble in a different timeline and Goku having to rescue her. Along the way, they discover new forms of power and new allies.
There's a fanfiction where Goku accidentally ends up in West Kai's realm in a rather comical way. This sets off a series of events that lead to them getting closer. It's filled with action and light - hearted moments, showing Goku's naivete and West Kai's patience.
It could also be a symbol of a new power - up. In the Dragon Ball series, new physical changes often lead to increased power. So, getting his tail back might mean that Goku is about to reach a new level of strength. Maybe he'll be able to transform into a new form that is related to his Saiyan heritage and the presence of the tail. This could give him an edge in future battles against stronger opponents.
One common theme is the clash of different power systems. Star has her magic from the 'Star vs the Forces of Evil' universe, and Goku Black has his Saiyan powers from Dragon Ball. Another theme could be the exploration of good and evil. Goku Black is a villain, so stories might focus on how Star and her friends deal with his malevolence. Also, the idea of interdimensional travel can be a theme, as Goku Black is from a different universe in Dragon Ball and would have to cross into Star's world.
Well, I don't have a specific title off - hand. But a good place to start looking for 'Star vs the Forces of Evil Goku Black' fanfiction is Archive of Our Own. They have a wide range of fan - created works. You can filter by the relevant fandoms and look for stories that incorporate both elements in an interesting way, like maybe a story where Goku Black ends up in the dimension of 'Star vs the Forces of Evil' and causes chaos.