In the manga, Goku managed to kill Zamasu by combining his strength with Vegeta and performing a joint attack. They also exploited Zamasu's weaknesses to gain the upper hand.
A common theme is power - seeking. They are often depicted as constantly striving for more power and ruling over the universe. Another theme is their unique bond, whether it's a friendship or a more sinister partnership.
One popular 'goku black x zamasu fanfiction' is 'The Dark Alliance'. It delves deep into their partnership and the chaos they create in the universe. Another interesting one could be 'The Merged Power', which explores what would happen if they combined their powers in different ways.
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.
Zamasu meets his end in the manga because he underestimates the strength and strategy of Goku and Vegeta. They exploit his weaknesses and deliver the final blow that finishes him off.
Redemption could also be a theme. Although Zamasu in the original was quite villainous, a female Zamasu in fanfic might be on a journey of self - discovery and redemption. She could start as a bad character but gradually change due to certain events or interactions in the story.
She might be depicted as having a complex personality. On one hand, she could have a cold and calculating side due to her divine or self - proclaimed superior nature. On the other hand, there could be a hidden vulnerability that only the male reader gets to discover. This duality can make for an interesting exploration in the fanfic.
Well, in fanfics involving Female Zamasu and a male reader, it often explores a unique dynamic. The relationship could be based on the contrast between Zamasu's divine or complex nature and the more ordinary male reader. It might involve themes of power, redemption, or a journey of self - discovery for both characters.