Saber would probably be quite shocked at first. She's used to Shirou as a male, and this sudden change would make her re - evaluate their relationship. Rin might be more intrigued and try to figure out what caused the transformation. Archer would likely be a bit dismissive at first, but then realize that Shirou in this new form still has the same determination. Illya might find it really funny and tease Shirou a lot about it.
Well, one possible plot could be that Shirou wakes up one day as a girl and has to deal with all the new physical and social changes. His friends might be really confused at first, like Saber who would be very surprised to see her master in a different form. Shirou, now as a girl, might struggle with things like wearing dresses and having different hormonal emotions. And he would have to face enemies in this new form too, which could lead to some really interesting battle scenes where his opponents underestimate him because he's now a girl.
Blake would probably be very shocked at first. Given their past relationship, she might feel a strange mix of emotions. She could be sympathetic towards Adam's situation, but also be cautious because of their history. Yang, on the other hand, might be more distrustful initially. She would see Adam as a potential threat still, even in his new form. Ruby might be the most open - minded, trying to see the good in Adam and offer help if needed.
The other characters' reactions would be diverse. Bakugo might initially be very confused and maybe even mock Midoriya a bit, but deep down he'd still see her as a rival. Uraraka would probably be very empathetic and quickly become a good friend to Midoriya in her new form, helping her with things like getting used to the new body. And All Might would be very supportive, seeing it as just another obstacle Midoriya has to overcome in her journey to become a great hero.
Some of the male characters might be a bit flustered around Naruto as a girl. For example, Kiba might act differently, not quite sure how to interact with her in this new form. Hinata, on the other hand, could become even more shy. She already had a crush on Naruto as a boy, and now with Naruto as a girl, her feelings could be even more complex. The Akatsuki members, if they were to encounter Naruto in her new form, might underestimate her at first. But Naruto, with her indomitable spirit, would soon show them that she's still a force to be reckoned with, regardless of gender. And the reactions of the characters would not only be about how they see Naruto, but also how Naruto's new form affects the power dynamics and relationships within the Naruto universe.
His projection magic might be affected by the different magical rules in the Highschool DxD world. Maybe it becomes more powerful or has some new limitations. For example, projecting holy swords could have a different energy cost or be more effective against certain types of devils or fallen angels.
If Shirou Emiya were reincarnated as a girl in fanfiction, the story could take an interesting turn in terms of romance. She might attract different suitors or have a different approach to love. Maybe she would be more reserved or more bold in expressing her feelings, depending on how the author writes her personality. And in combat, she could bring a unique feminine touch, like using grace and agility in a different way compared to her male self.
Shirou would fit in as a powerful and unique addition. His combat skills and magecraft would make him a formidable ally or opponent. He could use his projection abilities to create various weapons and tools, which would be very useful in the battles that often occur in the Highschool DxD world.
His character development would likely be different as a girl. For one, he might be more in tune with his emotions. In his male form, Shirou often represses his feelings. As a girl, she could be more open to exploring her emotional side, which could lead to a deeper understanding of herself and others. This could also affect her relationships, as she might be more vulnerable and trusting, or she could be more guarded depending on her experiences.
It could be interesting. Maybe Naruto would have Shirou's self - sacrificing nature. He might use Shirou's projection magic in a Naruto - like way, like projecting kunai or shuriken instead of swords. And his fight scenes could be a blend of Naruto's ninjutsu and Shirou's combat style.
In fanfiction, Shirou Emiya could be integrated into the Highschool DxD world by being a wildcard factor. For example, he could be a human with powers that no one expected. His strong sense of justice would lead him to get involved in the conflicts between the different supernatural groups. He might even form his own group of allies, made up of both normal students and supernatural beings who believe in his cause.