You might be surprised how this multi-chapter Goku/Gohan was inspired.   
I have another fanfic I’ve been working on FOR YEARS – unfortunately it’s a little too RL to just willy-nilly post – or at least it is supposed to be more realistic. 
So, I have that other too-serious-story going, and one of the things coming out of the UST in it is Goku or Gohan fantasies. 
Soldier Boy started out as one of that-particular-story’s-Gohan’s fantasies – and then grew to 9+ chapters. 
In this particular case, the Gohan from the other story was trying to find a way to make it…reasonable for Goku to realize he found Gohan attractive in a sexual matter.  Thus a fantasy, thus a one timer, that then begged for so much more I couldn’t tell it no.   
O.o  My muses might just perpetuate themselves if I’m given enough breathing room.   
Now I understand why they call them plot bunnies.   
o.O  Scary.