Dreams.

I often have a recurring dream where random characters, which I blatantly plagiarized from other works, play an active role in the plot of my comic. Every time, I wake up in a cold sweat.
Perhaps this is related to the fact that I seriously considered the idea of creating a small fan comic about Sailor Moon for a while, with the goal of fixing some things that annoy me in the original in the most consistent way possible. I eventually abandoned the idea, but the feeling lingered.