Well, Spy x Family fanfiction can be really interesting. Some fanfictions might explore different relationships between the characters in more depth. For example, they could focus on the bond between Anya and Loid in a new situation that wasn't shown in the original manga or anime. It's also fun to see how authors play with the spy and assassin themes in unique ways.
Loid is also a top pick. His stoic and secretive personality would make his reactions to unexpected situations or revelations in a react fanfic very engaging. He could be reacting to Anya's school life shenanigans or Yor's attempts at being a more 'normal' wife, and his internal struggle to maintain his cover while dealing with these emotions would be fascinating to explore.
One idea could be the Forgers reacting to an alternate universe where their secret identities are all exposed at once. It would be full of chaos and interesting character interactions.
One interesting Spy x Family React fanfiction could be where the Forger family reacts to different spy gadgets. It's fun to imagine Anya's excited reactions to cool spy tech. Another might be them reacting to different types of missions that Loid has been on. It gives a new perspective on his character.
If RWBY were to react to Spy x Family fanfiction, they would bring their own perspectives. Ruby, with her innocent and curious nature, would likely be intrigued by Anya's telepathic abilities. Weiss, being more refined, might analyze the political and social aspects of the Spy x Family world. Blake, having experienced secrecy herself, would empathize with the characters hiding their true identities. Yang would enjoy the comical moments and the action - packed sequences, like when Loid does his spy stunts.
You can start by looking on fanfiction websites like Archive of Our Own. Just type in 'Spy x Family React' in the search bar, and it'll show you a bunch of relevant stories. Check the ratings and reviews to see which ones are popular and well - liked.
A fanfiction about Anya's school adventures sounds really cool. Anya's experiences at school are already full of humor and chaos in the original work, so in fanfiction, it could be even more exaggerated. Maybe she'll get into some crazy trouble with her classmates that involves her telepathic powers in a new and hilarious way.
In a Giyuu x Shinobu fanfic, the setting and plot can vary widely. Some might be set during the main events of the Demon Slayer universe, with them facing demons together. Others could be more of an alternate universe story, where they meet under different circumstances, like in a modern - day high school AU. The fanfic could also delve into their backstories and how those experiences shape their relationship. For instance, Shinobu's past with her sister could play a role in how she opens up to Giyuu, and vice versa for Giyuu's own traumas.
I would recommend 'Whispers of the Heart' for Giyuu x Shinobu fans. This fanfic focuses on their unspoken understanding. It's full of small moments that build up their relationship, like when Shinobu leaves a small flower on Giyuu's doorstep as a sign of her care. Also, 'Shadows and Sunlight' is worth checking out. It has a great plot that involves them having to go on a secret mission together and how that journey changes their relationship from colleagues to something more intimate.