If Crowley got sick, he'd probably be really grumpy about it. He's not used to being vulnerable. But Aziraphale would be there to make sure he rests and gets better. Maybe Aziraphale would bring him books to read while he's bedridden. And Crowley would complain about the books but secretly enjoy the company.
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, in some sick fanfiction involving Jackson from Got7, the story could revolve around a sick fan who is a huge Jackson stan. She (or he) could be in the hospital and Jackson, through some miracle, finds out. He then visits the fan and brings some of his own positive energy, which helps the fan recover faster. It's a sweet concept that plays on his image as a kind-hearted idol.
One common theme is the exploration of their relationship. Given their different personalities in the original work, fanfictions often focus on how they bridge the gap between them, like how Giyuu's stoicism and Shinobu's more cheerful yet calculating nature interact.
His character is often portrayed as very caring. For example, if a fan is sick, he might drop everything to be by their side, bringing them medicine and food.