Well, one big challenge is combining the different power systems. In Fate Stay Night, you have magic and Servant abilities, while in Halo, it's all about advanced technology and physical combat skills. Figuring out how to make these two coexist in a believable way is tough.
Characterization can also be a struggle. The characters from Fate Stay Night have very distinct personalities shaped by the magical world they live in. The Halo characters are more military - minded and used to a different kind of life. When you bring them together, you have to make sure their interactions are consistent with their original personalities while also allowing for growth and change in the new crossover situation.
There's also 'Fate in the Halo Universe'. This one is about how the Fate characters find themselves in the Halo setting. It explores how they interact with the UNSC and the various alien species. For example, Saber's honor code clashes and also meshes in interesting ways with the military values of the Spartans.
One challenge is to blend the two very different settings. Naruto has a world of ninjas and chakra, while Halo is a high - tech, space - faring universe. Making the two coexist in a believable way is tough.
One common theme is the clash of power systems. Since Bleach has its spiritual powers and zanpakuto, and Fate Stay Night has magic and Servants, seeing how these interact is a big draw. For example, how would a Servant fare against a Hollow in Bleach? Another theme is the exploration of different ideologies. The characters in both series have distinct beliefs and values, and fanfictions often explore what happens when these collide.
A cool 'fate stay night crossover fanfiction' idea might be a crossover with 'Final Fantasy'. The different classes and magic systems in Final Fantasy could blend well with the Fate universe. For example, a character from Fate could learn the job classes from Final Fantasy. Also, a crossover with 'Persona' could be interesting. The Velvet Room and the concept of personas could be integrated into the Fate world, adding a new layer of mystery and power to the story.
In these crossovers, the theme of growth is quite common. Shirou starts as his normal self but through his experiences in the new world, he grows as a character. For example, in a crossover with the 'Naruto' world, he may learn new combat techniques and also gain more understanding of different kinds of power. Another theme is the exploration of new power dynamics. How his power compares to the powers in the new world, like if he's in the 'Bleach' universe, how his abilities stack up against Soul Reapers. And the theme of moral dilemmas also exists. He may face situations where the moral code of the new world challenges his own.
One unique feature is the combination of different universes. For example, when Saber is crossed over with a modern - day setting, it creates a contrast between her medieval values and the contemporary world. This leads to interesting character development as she has to adapt.
Well, perhaps in this crossover fanfiction, the power systems of both could merge. For example, the magical abilities of the Fate Stay Night characters could combine with the Freezing characters' abilities. Let's say Saber's Excalibur could be enhanced by the energy manipulation skills of a Freezing character. And there could be a love triangle between a Fate Stay Night male character, a Freezing female character, and another character from either universe, which adds a lot of drama to the story.
In a Fate Stay Night Skyrim crossover, Archer could be summoned by a powerful mage in Skyrim. Archer would find the concept of the Thu'um fascinating as it's a form of magic he's never encountered. He could start exploring Skyrim, looking for ways to use his own abilities in conjunction with the local magic. He might get involved in the civil war between the Stormcloaks and the Imperials. His strategic mind could help whichever side he decides to side with. And when the dragons return, he could use his Unlimited Blade Works to create weapons specifically designed to fight dragons, like blades that can pierce dragon scales more easily.
The most interesting part is the combination of different powers. In RWBY, we have the unique Semblances and in Fate Stay Night, there are powerful Servant abilities. When these are combined in a crossover fanfiction, it creates really exciting battle scenarios.
A crossover with the Persona series is also quite popular. The themes of the inner self and combat against otherworldly entities in both series can be blended together. The characters from Fate Stay Night could potentially enter the Metaverse from Persona and interact with the Persona users. This could lead to some really cool battles and character development.