Need inspiration for a medieval game?

Ok, so my friends and me are in the middle of designing a stick figure based 2d rts game. Corbin's working with gimp to make the computerized imagery, Cody and Corbin are working on coding, Aedan, Calum and me are working on artwork, and i have to do the story by myself. Corbin wants me to do something with hell or demons, he thinks it would be pretty cool. (Me too) So, I can't even work it in to the story, I have no idea what they are going to use, what they look like, or what there castles would look like. Your in the part in the story where you partner with the king to take out a large group of barbarians. Maybe they summon them or something? Idk. I have Aedan (close friend) coming over to help, but its not till tomorrow. Do you guys have any ideas?