There's also something worth being said about the fact that he definitely watched Guren Lagaan and got far enough into the anime to cringe at the "Don't believe in me, believe in the me that believes in you!" line when Dave and Karkat confess. And that he chooses to dress as Kamina instead of Simon, the actual main character. Dirk doesn't have a Kamina in real life and can only idolize his bro from afar since he and alt!Dave never actually knew each other. So I can see him just deciding to go "Fuck it, I'LL be Kamina. I don't need someone around to inspire me, I can do it myself!" and literally dressing up as the show's single embodiment of hope.