What are some interesting ideas for Re Zero crossover fanfiction?

Another plot could involve the Pleiades from Overlord. They end up in Re:Zero and are mistaken for some sort of magical spirits. Subaru tries to enlist their help in his quest to save Emilia. The Pleiades, with their combat skills and unique abilities, could change the power dynamics in the Re:Zero world and also introduce new technologies and magic concepts from Overlord.

Another idea is to write a fanfiction where the roles are reversed. Make Emilia the one with a special power and Subaru as the more 'normal' character who has to support her. It could be fascinating to see how Emilia would handle the burden of a power like Return by Death and how Subaru would adapt to being in a more supportive role.

One idea could be that Subaru somehow gets the Geass power. He could use it to try and save Emilia in a more decisive way, but he also has to deal with the moral implications of the Geass, just like Lelouch did. This would create a really interesting dynamic as Subaru is already a complex character dealing with his own set of challenges.

Perhaps Shirou from Fate Stay Night could find himself in the Re Zero world. He might use his skills as a mage and his determination to help Subaru in his quests. Their different outlooks on life and combat could lead to some interesting character development as they learn from each other.

You could create an OC who is a master of illusions. This character could use their powers to deceive both enemies and allies, and their backstory could involve being an outcast from their own illusionist clan because they refused to use their powers for evil. In the Re:Zero world, they could help Subaru by creating diversions during battles or by using illusions to uncover hidden truths.

A cool Horizon Zero Dawn crossover fanfiction idea is a crossover with the Legend of Zelda. Picture Aloy in the world of Hyrule. She could use her skills to solve some of the puzzles there and maybe help Link in his battles against Ganon. She might be intrigued by the different types of magic and technology in Hyrule compared to her own world. Also, her spear - fighting skills could be a great addition to Link's combat techniques.

One interesting idea could be the interaction between the different power systems of 'Overlord' and 'Familiar of Zero'. For example, how the magic in 'Familiar of Zero' might interact with the various abilities of the characters in 'Overlord'.

Another plot could involve Ultraman Zero crossing over to a post - apocalyptic Earth. He finds a group of survivors who are fighting against mutated monsters. Zero has to use his powers not only to defeat the monsters but also to help the survivors rebuild their society, teaching them about hope and perseverance.

Perhaps in the fanfiction, Zero and Kiryu both get cursed by an ancient magic. The curse gives them some of each other's traits while also weakening their own original powers. This forces them to rely on each other more than ever. They go on a quest to find the source of the curse and reverse it. Along the way, they learn about each other's pasts, values, and what really drives them, leading to a deep friendship or respect for one another.

A plot could involve a werewolf being sent to the 'familier of zero' universe. The werewolf's abilities would be a mystery and source of both fear and fascination. They could end up being hunted or befriended depending on how the story unfolds. It could also lead to a discovery of a common enemy between the two universes.