Another idea is that Shirou, as an angel, has some sort of connection to a powerful artifact in the Highschool DxD world. This leads him to enroll in the school to search for it. During his search, he has to deal with the hormonal chaos of high school, the different species vying for power, and his own angelic duties that keep pulling him in different directions.
One plot idea could be Shirou Emiya, as an angel, arriving at the Highschool DxD world and getting involved in the ongoing power struggles. He might use his skills from the Fate series to help out the various factions while also trying to maintain his angelic identity.
Well, Shirou could form an unlikely alliance with some of the characters in Highschool DxD. Maybe he teams up with Issei and his group. Since Shirou has a strong sense of justice, he could help them in their battles against stronger enemies. He might also teach them some of his combat techniques, like how to better utilize their own powers.
One idea could be Shirou using his projection magecraft in the Highschool DxD world to create unique weapons during battles against the devils or fallen angels. For example, he might project Excalibur to fend off a powerful devil attack. Another plot could involve Shirou forming an alliance with Issei and his group, teaching them about his different combat techniques and how to better strategize in fights. He could also have a romantic sub - plot with one of the female characters from Highschool DxD, like Rias, where his noble and self - sacrificing nature attracts her.
A plot could involve Shirou being transferred to the Highschool DxD school. He quickly catches the attention of Rias and her peerage. His different style of combat and his unwavering determination might lead to some friendly rivalries within the group. He could also introduce some new concepts of magic that the DxD characters have never seen before, like his ability to reinforce objects. And he may find himself in the middle of the power struggles between the different factions in this new world.
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.
One great fanfiction could be 'Shirou's New School Adventure in Highschool DxD'. In it, Shirou uses his skills from the Fate series in the chaotic world of Highschool DxD. He might form unique alliances with the characters there, like Issei. It's an interesting read as it combines the two different universes' concepts.
In this fanfiction, Shirou might be seen as an enigma. His calm and collected demeanor would be different from the more boisterous characters in Highschool DxD. He could potentially be a mediator between the different groups, given his own experiences with complex moral situations in the Fate series.
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.
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.
One common plot idea is an angel falling in love with a devil, which goes against the norms of their respective worlds. It creates a lot of drama and tension as they try to navigate their relationship while also dealing with the expectations of their own kind.
Another plot could be that Shirou discovers a new, highly competitive gamer community. He starts from the bottom but his determination and strategic thinking, which he has from his heroic deeds, help him rise through the ranks. He might make new friends and rivals in this community.