There’s often an old saying, the more secrets there are, the more people want to pry…and the stronger the bond between the two persons, the more it turns us on…I assume this theory has brought about this genre of 萌え[moe]…yes, that is 主従萌え[shujuu-moe]. 主従[shujuu] means master-servant relationship. Technically we can say 主従関係[shujuu kankei]. For some reason, I feel this kind of thing is getting popular more and more…come to think of it, we already have a butler cafe, don’t we? But then what is so special in this? Speaking of master-servant relationship anime, I can think of Zero’s Familiar, Kimi ga aruji de shitsuji ga ore de, Himawari!, and so on…and mentioning some certain pairs, Haruhi×Kyon, Shuurei×Seiran in Saiunkoku monogatari, Sebastian x Ciel in Kuroshitsuji. If it gets doujin staff, it could be uncountable. Mostly, a master should be very cold and arrogant(yes, defintely tsundere), and a servant has to obey (his?)master…No matter how hard the master is, no matter what the master does to the servant, the servant has to respect and follow the master…
Having said that, the master actually cares about his servant more than anybody else, and the servant would be sure of that. That’s why the servant can endure the tough work his master gives. I daresay the master is even sure that his servant never betrays him, and the servant knows his master can’t do anything without him, he has nobody to help him. To anyone who doesn’t know this weird relationship, it seems to be very awful. But actually the two persons are bound by a strong bond…If you want to pry the deep secret, yes, you might have a 主従萌え.
Mostly in this kind of doujin manga, a master is so hard to understand and always swears him. But his servant shall do whatever he asks. When almost all the people around him leave him, and when he really really needs someone to be by him, only his servant stands by him…and finally the master shows his dere-side. Whoa, this is something like お約束 in this genre, though.
One more thing, in BL circles mostly a master would be uke, and his servant would be seme. There might be other way around, but only when they do “it”(maybe almost the last scene), the servant gets very aggressive. Yes, this is what’s-called 下剋上オチ[gekokujou-ochi, gekokujou conclusion].