Friendship is a big theme too. Characters from different universes in Sailor Moon crossover fanfic often become friends and learn from each other. They support each other in battles and in personal growth. Also, the theme of saving multiple universes is quite common. Since it's a crossover, there are usually threats that endanger both the Sailor Moon universe and the other crossed - over universe.
Love and romance can also be a theme. Sometimes, characters from different universes fall in love. This adds an interesting dynamic to the story as they have to deal with cultural differences and the fact that they come from different worlds. It can also lead to some really sweet and heart - warming moments in the fanfic.
Power is a big theme. The powers of the Sailor Scouts, which are based on elements like the moon and stars, are different from the vampiric powers in Vampire Knight. In crossover fics, there's often a comparison or a combination of these powers. Also, the idea of good vs evil is common. Sailor Moon and her friends are the defenders of love and justice, while vampires in Vampire Knight are often seen as more morally ambiguous. So seeing how they interact in the face of threats is a theme. Sometimes, there's also the theme of transformation. Both series have elements of transformation, and in crossovers, it can be interesting to see how the two types of transformations interact.
One common theme is power combination. Writers often explore how the powers of Sailor Moon characters combine with those from the other crossover universe. For example, in a Sailor Moon and Dragon Ball Z crossover, they might look at how Sailor Moon's magic could work with the energy - based attacks in Dragon Ball Z.
Another theme is the power of friendship. Both Sonic and Sailor Moon series value friendship, and in crossovers, it's often about how the characters from both sides form bonds and work together. For example, Sonic's loyalty to his friends and Sailor Moon's strong relationships with the Sailor Scouts combine to create a united front against common enemies.
Another theme is the teamwork between the two sets of characters. For example, the Sailor Guardians are used to working together in their own way, and Sam and Dean Winchester have their own dynamic. In these crossovers, they have to find a way to combine their skills and strategies to face the threats. Usually, they start off a bit at odds but gradually learn to trust and rely on each other. This theme of building new relationships across different universes is quite prominent.
One common theme is self - discovery. The OC daughters often start out not fully aware of their powers or their place in the Sailor Moon universe, and the story follows their journey to figure these things out. For example, they might discover they have a special connection to a certain Sailor Scout.
One common theme is the combination of powers. Since both series have characters with unique abilities, fanfictions often explore how these powers can work together. For example, the Saiyans' strength combined with the Sailor Scouts' magic.
Power and responsibility are often explored. Since Queen Serenity has great power, the OC might be learning about the responsibilities that come with power, just like the Sailor Scouts do. Also, the theme of sacrifice can be present. Queen Serenity is known for her great sacrifice, and the OC might be faced with similar situations where they have to make difficult choices for the greater good. Additionally, the idea of destiny is common. The OC may be trying to figure out their place in the grand scheme of things in the Sailor Moon world which is often guided by destiny.
Another fanfic concept is that there's a threat in Gotham that has a connection to the Moon Kingdom's past. Sailor Moon travels to Gotham to investigate. There, she meets Batman, who is initially skeptical of her magical powers. But as they start to work together, they realize that their skills are complementary. For example, Sailor Moon's ability to heal could be useful for Batman's injured allies, and Batman's detective skills could help Sailor Moon figure out the mystery behind the new threat.
One idea could be a story where Goku and Sailor Moon team up to fight a common enemy. Maybe a powerful demon that is threatening both their worlds. They could learn from each other's fighting styles, like Goku showing Sailor Moon how to better use her physical strength and Sailor Moon teaching Goku about the power of friendship and love in combat.
One common theme is the combination of different magical systems. For example, mixing Sailor Moon's lunar magic with other supernatural powers like witchcraft or demon magic. Another theme is the exploration of alternate universes where Sailor Moon characters interact with a wider range of supernatural beings.