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.
A common theme is power combination. Writers often explore how Naruto's powers, like his Rasengan or Shadow Clone Jutsu, can be combined with the Sekirei's powers. Another theme is the clash of cultures, as the ninja world of Naruto and the modern - yet unique - world of Sekirei collide.
Another theme could be the cultural differences between the two universes. The Final Fantasy world has its own set of values, and the Sekirei world has its own. Fanfiction might play with how characters from these different cultures interact and adapt. For example, Sephiroth might find the concept of Sekirei pairs very strange at first. It can lead to interesting character development and relationship building within the story. And this often makes for an engaging read as the author tries to blend these two very different worlds together in a believable way.
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.
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.
Power - up is a common theme. Since Naruto is godlike, it usually involves him having super - enhanced powers in the Sekirei world. Another theme could be relationship building, like how he interacts with the Sekirei characters.
One popular Shirou is a Sekirei crossover fanfiction might be 'Shirou's Sekirei Adventure'. In this type of crossover, Shirou's character traits from his original story, like his determination and swordsmanship skills, could blend interestingly with the Sekirei world's unique elements such as the Sekirei battles and the concept of Ashikabi. Another one could be 'Shirou in Sekirei's World'. These crossovers often explore how Shirou would adapt to the Sekirei universe and how his presence might change the existing storylines in the Sekirei world.
One common theme is power and its consequences. Since Shirou has godlike powers in these fanfictions, it often explores how such great power affects him, whether it corrupts him or makes him a better person.
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 common theme is her relationship with other Sekirei. Since she is a significant character in the Sekirei world, many fanfictions explore how she interacts with her peers, whether it's in a friendly or competitive way.