In the vein of VN layman psychology, I always liked the theory that Hisao's in a coma after all, and his Yamaku adventures might represent a cathartic process for him to find his way back into consciousness and life - kind of like in The Odyssey, a Canadian kid's TV series that I used to watch when I was a kid; I guess it sorta introduced me to metanarratives at an early stage, too.
Anyway, if I ever had to write a piece of fanfiction for KS, it would be a frame narrative, depicting how Hisao is comatose after all and - contrary to what he notes in the intro chapter - Iwanako did not stop visiting him, but instead continued to visit him and talk to him. He unconsciously constructs the five/six KS girls from what she tells about herself, and gets cues for the narrative arcs/paths from her stories from school and home.
Since I'll never write this story, I'd like to request an artistic rendition of it. I could see an image of an pale, slightly emaciated and maybe not even recognizable Hisao in bed (frail body outlined against the bedsheets) with Iwanako sitting next to him, looking out of the window. Bonus points for giving her a complicated/interesting expression (gloomy and serene?), interesting shading/lighting (no lights on, stars outside?) and maybe a fragment of her narration, something that dimly reminds one of KS without being a direct quote.