I'm not going to write a fanfic100 challenge specifically on Heiji and Kazuha, if that's what you're asking. I don't think I can even make two claims from the same fandom >:D

Will they pop up in there at some point? ...hard to say, although I'm really not sure who else I'll use the prompt "green" for. It is sort of their color... *ponders*

You'll have to ask Quinn that :)