All of the themes in this piece are themes in Ashboy's "Fugue of the Storm": https://musescore.com/ashboy/scores/25817
The description of the song starts off: "First of all, I KNOW THAT IT'S NOT A FUGUE! I am just attached to that title." I read that and thought, "Well, why can't it be?" So I decided to turn FOTS into a fugue. That's about all there is to it.
DISCLAIMER: I have no idea how to write fugues. I can sort of write an exposition to a fugue, but that's about it. I basically just made everything else up, trying to make it sound like a fugue :)