It's a bit confusing description ye, but the previous season's (1st and träumend's, around 2004) "antagonist", that being Suigintou is the "hero" in Ouvertüre, mostly set in a flashback in 19th century London. That of which we now have its first DVD release available. So I guess it's correct
Weird choice of words, antagonist and hero indeed
Edit: Hmm... hit me just now, calling 2 episodes a series....