One consequence could be that it attracts unwanted attention. Since Excalibur is a very powerful weapon, it might draw the notice of powerful villains in the RWBY world. Another consequence could be that it changes the power dynamics among the characters. If Shirou is suddenly very powerful with Excalibur, it could make other characters feel overshadowed or they might have to adjust their fighting styles to work with him.
Well, in RWBY fanfics involving Shirou and Excalibur, it often brings a unique blend of the Fate universe and RWBY's world. Shirou's connection to Excalibur can add a lot of depth. For example, his skills and the power of Excalibur might be portrayed differently in the RWBY setting. Maybe he uses it to fight against Grimm, and the way he wields it could be adjusted to fit RWBY's more acrobatic combat style.
In RWBY fanfiction, Shirou using Excalibur could be a very interesting scenario. Maybe he uses it in a way that combines his own sword - fighting techniques with the unique combat styles of RWBY. For example, he might incorporate some acrobatic moves like the characters in RWBY do while slashing with Excalibur. And he could use the power of Excalibur to break through tough Grimm defenses, given that Excalibur is often depicted as a very powerful weapon in its original context.
It fits in an interesting way. Shirou's Excalibur can be seen as an out - of - place yet powerful element. It might disrupt the normal flow of RWBY's world, but also offer new possibilities for combat and storylines. For example, it could be the key to defeating a new, extremely powerful type of Grimm that the regular RWBY weapons can't handle.
One possible fanfiction could involve Shirou being transferred to the Highschool DxD world and somehow obtaining Excalibur. Maybe he has to use it to defend the school from a new threat that the regular characters can't handle on their own. This would lead to some interesting interactions between Shirou's abilities and the magic and powers in the Highschool DxD universe.
Perhaps Shirou time travels to a time when Excalibur was lost. His mission could be to find and retrieve the sword. Along the way, he meets various characters from different time periods who either help or hinder his quest, and through his journey, he discovers new aspects of his own identity related to the sword.
A simple plot could be that Shirou accidentally activates Excalibur's time - traveling ability. He finds himself in Camelot and has to adapt to the new environment. There, he meets King Arthur and other knights, and his knowledge from the future helps him in various challenges while also learning about the true power of Excalibur.
The plot could be that Shirou is summoned to the Highschool DxD world by accident. He discovers that his connection to Excalibur is stronger here. He is then forced to participate in the power struggles between the different factions. He uses Excalibur to protect the innocent students in the school from the more aggressive supernatural elements. Along the way, he might fall in love with one of the female characters in the Highschool DxD world, adding a romantic sub - plot to the story.
One common theme is the exploration of Shirou's character in the RWBY universe. How his skills and personality interact with the RWBY characters and the world around them.
One consequence could be that it makes him a more formidable opponent. His enemies would have to rethink their strategies as he can now teleport.
One common theme is the clash of different power systems. Shirou's magic in contrast to the Aura and Semblance in RWBY. Another theme could be the characters' moral compasses. Since Shirou has a strong sense of justice, seeing how he interacts with the RWBY characters' own values is interesting. And of course, the fish - out - of - water scenario, like Shirou being suddenly dropped into the RWBY world and having to adapt.