The reaction of the gods would be diverse. The muses might be intrigued and want to inspire Percy further. Dionysus, the god of wine and celebration, might see Percy's singing as a great addition to his wild parties. However, some of the more serious and war - like gods, such as Ares, might scoff at it, thinking it's a useless skill for a demigod. But overall, Percy's singing would definitely stir up a lot of different emotions and reactions among the gods in the fanfiction world.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for 'female giyuu fanfiction' using the search bar. Another option is FanFiction.net, which also has a good number of such stories.
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.
Well, there's 'Giyuu and the Mysterious Female'. In this fanfiction, a female character with special powers enters Giyuu's life and they go on adventures together. Also, 'Female Friendship with Giyuu' focuses on the platonic relationship between a female and Giyuu, showing how they support each other in the demon - slaying world.