Hey there, it's me. Daniel.
So, I desire help in creating a Fanfiction, but whenever I try to write one, my mind is a blank slate, with only pancakes and rainbows etched onto it. However, when I am doing something other than write, like spriting, my brain is overflowed with ideas, overriding my ability to think logically. If anyone knows how I can conquer this, please reply.
Well, there are multiple ways, and what works best varies from person to person. I would suggest however trying to write out those ideas you have when they happen; and it doesn't have to be properly written up or anything. Could be in a mind map or point form or the like. That way you might get it out of the system so you can do spriting or whatnot (or maybe it'd just get you in the mood for writing too; again it depends). Later on when you want to write but are stuck on what to write about look at those notes and try to expand on them. Ask questions (what if ___ happened? How would this character react?) and go from there.
(I think I wrote some more on this in the first post in the Plot Bunny thread sticky at the top of this section as well, in case that proves useful for you).