A Shirou crossover fanfic could involve him crossing into the world of Harry Potter. Imagine Shirou's magic system interacting with the magic of Hogwarts. He could perhaps teach the students there some unique combat techniques. Or a crossover with the world of Naruto, where Shirou's swordsmanship and his ability to trace weapons would be quite interesting in the ninja - filled world.
One idea could be a Shirou crossover with the Fate/Grand Order universe. He could interact with different Servants from various time periods and mythologies, creating new and exciting storylines. Another could be a crossover with the Nasuverse in general, where he meets characters from Tsukihime or Kara no Kyoukai.
Another concept is a more comical crossover. Shirou tries to adapt to the different rules and magic in the Fate Apocrypha world. He constantly gets into funny situations as he misunderstands the local customs and magic systems. For example, he tries to cook using Apocrypha - style magic ingredients and chaos ensues.
Another plot could involve Shirou reincarnated in a modern superhero world. He might struggle to fit in at first, but then realizes his abilities can be used to fight super - villains. His noble phantasm could be adapted in a unique way to combat the new threats in this world.
One idea could be that Archer is transported to an alternate universe where Shirou has a completely different personality. Maybe Shirou is a villain in this world, and Archer has to figure out how to deal with him. Another plot could involve them teaming up to fight a powerful, new enemy that neither could defeat alone. For example, a powerful mage from a different dimension who wants to conquer their world.
Another idea is that Kiritsugu summons Shirou because he foresees a future threat that only Shirou can prevent. This could involve time - traveling elements. Shirou might have to go back in time to change certain events. During this process, he and Kiritsugu would have to work together to figure out how to manipulate time without causing major disruptions.
Another plot idea might be to focus on Shirou's internal struggle during the Grail War in more depth. Show how his ideals are tested not just in battle, but also in his interactions with other Masters and Servants. Maybe he has to make some really tough moral choices that could change the course of the war.
A great Shirou Emiya crossover fanfic is 'Shirou and the Avengers'. Imagine Shirou in the Marvel Universe. He could project Mjolnir and use Thor's power. His selfless nature would fit well with the Avengers' values. Also, 'Shirou in the Dragon Ball Universe' is fascinating. He might train with Goku and learn ki control, while also showing his own swordsmanship skills against powerful foes in that universe.
One idea could be a crossover with Supergirl. They could team up to fight a common enemy like Lex Luthor who has some new, devious plan that threatens both Gotham and Metropolis. Another idea is a crossover with the Arrow. The two vigilantes could exchange fighting techniques and learn from each other's experiences in protecting their respective cities.
One idea could be a crossover with a popular fantasy series like 'The Lord of the Rings'. You could have planeswalkers from MTG enter Middle - earth. They might interact with the hobbits, elves, and dwarves. Another idea is a crossover with a superhero universe. Picture a planeswalker with superpowers like Superman or Spider - Man. They could team up with other heroes to fight a common enemy. Maybe a powerful Eldrazi that has invaded their world.
One idea could be a Spiderman and Iron Man crossover. Spiderman could team up with Iron Man to fight a new, powerful villain. Maybe they have to combine their tech and skills, like Spiderman using his web - slinging abilities along with Iron Man's high - tech gadgets to take on an enemy who can manipulate electricity.
A cool 'injustice crossover fanfic' could involve 'Injustice' and the 'Watchmen' universe. The gritty and morally complex world of 'Injustice' would contrast well with the unique and dark 'Watchmen' universe. Rorschach could find himself in the 'Injustice' universe and his uncompromising view of justice might clash with some of the characters there, while Dr. Manhattan's god - like powers could be a major factor in the story, either as a threat or an unexpected ally.