Well, Shirou in crossover fanfiction often shows his tenacity. No matter how strange or difficult the new world he is in, he doesn't give up easily. In a crossover with the Digimon world, he faces many challenges but keeps fighting. His loyalty is also a big part of his character. If he makes friends in the new world, he will be loyal to them and protect them at all costs. And his growth as a character is interesting. He may start with his basic set of skills from his original world, but as he experiences new things in the crossover world, he evolves, both in terms of his combat abilities and his understanding of different cultures and values.
There's a fanfiction called 'Kotomine and Shirou: United Front'. In this one, they are forced to team up against a common enemy that neither could face alone. The story delves deep into their relationship, starting from their initial distrust and gradually building towards a mutual respect and understanding. It's a great read for those who like character - development - focused fanfictions.
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 theme is identity. As Shirou enters the Miyuverse, he often questions who he is in this new context. He may compare his values from his own world to those in the Miyuverse. In a particular fanfiction, he struggles with whether his heroic ideals still hold true in this strange new place.
One common theme is the clash of two different worlds. Shirou comes from the Fate universe with its own set of rules, magic, and values, while the Sekirei world has its unique system of Sekirei, Ashikabi, and battles. Another theme is adaptation. Shirou has to adapt to the new rules and environment of the Sekirei world. For example, understanding how to form bonds with Sekirei as an Ashikabi.
Well, it could be about Shirou getting involved in the Sekirei battles. Maybe he uses his skills from his original story to help or compete in the Sekirei world. For example, his sword - fighting abilities might give him an edge in combat against other Sekirei or their Ashikabi.
One possible scenario in such a fanfiction could be Shirou Emiya's unique abilities from the Fate series being introduced into the Highschool DxD universe. His projection magic might cause quite a stir among the devils, angels, and fallen angels in that world.
Another good choice would be Harry Potter. Imagine Shirou in the wizarding world. He could use his tracing ability to create magical items, and he could also learn new spells from the Hogwarts professors. They could team up to fight against dark wizards.
One popular miyuverse shirou crossover fanfiction is 'Shirou's New Adventure in Miyuverse'. It combines the unique elements of the Miyuverse with Shirou's character in an interesting way. The story often has him facing new challenges and making unexpected alliances within the Miyuverse setting.
It could be a powerful Sekirei who sees Shirou as a threat to the Sekirei Plan. This Sekirei might be very traditional in their views and not like the idea of an outsider like Shirou interfering.