Boys can develop good sleeping habits by having a regular sleep schedule. Go to bed and wake up at the same time every day. Also, creating a comfortable sleeping environment, like a dark, quiet and cool room, helps a lot.
Perhaps the boy has a routine of taking a long afternoon nap. One day, his friends came to visit unexpectedly. The roommate tried to wake him up gently, but he just wouldn't budge. His friends ended up waiting for him to wake up on his own while having a great time chatting with the roommate.
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.