5) Master/servant dynamics. Another thing that can be really bad when done wrong, but amazing when done right. I like it when there's a strong enough bond between the master and the servant that the power dynamics start to blur- particularly if the servant is the more capable/powerful of the two (see: FFVII again, and Vassalord).

Are you reading Fumi Yoshinaga already? She has a definite fondness for doing twisty and uncomfortable-but-compelling things with relationships with big power differentials, including master/servant pairings -- and she'll then throw in so many additional twists of age differences and quasi-familial relationships that trying to figure out just who really has the most power gets incredibly blurry.

(Mmmm, Vassalord. *licks yummy Rayflo icon*)