I think these two terms are not so old yet, but surely we have used them without the first letter, ド[do]. At any rate, エス[esu] is actually S, and エム[emu] is M. So…caught on, haven’t you? Yes, S stands for sadist and M stands for masochist. For some reason, it’s getting common to put ド ahead of each. I’m not sure why, though. Well, ド is used to emphasizes how excessive it is. Mostly, it is written in katakana, but in kanji, it should be 度. Having said that, there are few adjectives to function with ド. I can think of アホ[aho”stupid“], へたくそ[hetakuso”not good at doing something, or merely bad“], and so on.
These two terms are really common anywhere, not only in anime but also in the real world. People should be either ドエス or ドエム…Is there a middle point? If one is such a bully, and the other must be bullied by him/her. So let’s see some anime through this glass; speaking of ドエス characters, I can think of Haruhi Suzumiya(The Melancholy of Suzumiya Haruhi), Louise(Zero’s Familiar), Souryu Asuka Rangley(Evangelion). Sorry, I have mentioned those girls as ツンデレ[tsundere] characters. But wait, what about the other pair? Kyon seems to be relactant, but surely follows Haruhi, doesn’t he? However he whines, no matter what happens, he has to willy-nilly help her. Eventually, Kyon himself likes to do that. It’s not for the world, nor because Yuki Nagato told him to watch over her. So I guess Kyon must be ドエム. Forgive me, but otherwise he doesn’t follow Haruhi, right?
Also, what about Saito in Zero’s Familiar? Just because he was summoned by Louise as her familiar, Saito has to follow her. In the first place, yes. But as they get to know each other, Saito seems to enjoy himself even though he gets physically punished by her. So Saito must be ドエム, too.
After all, here’s a rule; if one of the pair is ドエス, the other should be ドエム. But what if both of them are ドエス or ドエム? How is the chemistry?