It's clearly the best Rozen Maiden so far and I'll be startled if Zuruckspulen outdoes it. It's dark, but excellent. It combines comedy and tragedy in the way that the anime franchise as a whole has been trying to do since the beginning, to at best intermittent success.
It's an origin story for Shinku and Suigintou, set in London at a time of top hats and horse-drawn carriages. I think of it as Sherlock Holmes's era, which suggests the 1890s. However there's also a modern-day framing story with all the regulars from Rozen Maiden: Traumend. We even know where to put it. It's after ep.6 since Suigintou's met Megu, but before ep.7 since Kanaria's still sneaking around undetected (and more importantly the fighting hasn't begun yet and everyone's still alive).
What are the dates for all this, incidentally? We've always known that the dolls are old, but here in addition we learn that they haven't been continuously awake since their creation. They'll wake up in one era to fight the Alice Game, then I think are sent back to sleep until the next one. That'll be why their personalities are still so childish, I'd imagine. Exactly how old are they, though? Let's assume that the anime's modern-day sections are contemporaneous with the manga's publication, i.e. 2002 or so. Suigintou said in Season 1 that she'd last faced Shinku 500,000 hours ago (i.e. 1945) and here Shinku mentions that things have changed a lot in the last 600,000 hours (i.e. 1933). Even that probably post-dates the main flashback story, though, which has horse-drawn carriages in London.
Anyway, the framing story is funny, which is a small triumph in itself. Rozen Maiden (especially the anime) keeps trying to be light and empty-headed, despite its underlying psychological horror. Sometimes the attempt fails. Here it succeeds. I laughed. It's only ten minutes, but it's good. In fairness there's lots of scope for comedy with these characters, but there's also always been lots of scope for trivial faff. The framing story also carefully includes more peripheral characters like the villains and that girl who used to be Hina Ichigo's medium and keeps associating with Jun in a way that suggests they might become boyfriend and girlfriend one day.
However we also see a couple of raw nerves with Shinku and Suigintou. Shinku dislikes a brooch that Jun buys her, to a degree that suggests distressing memories. (She hides her feelings from Jun, of course, with her usual coldness.) Meanwhile Suigintou really doesn't like roses.
Then, in the flashback, we see Suigintou in the beginning. She's pathetic, in every sense. She's broken. She can't walk and she's obsessed with their Father. She's not even at the poor level of the other Rozen Maidens, since their neo-fascist conditioning has taught them that they must be perfect to become Alice. Suigitou is imperfect. Thus, to the other dolls, she's the doll equivalent of sub-human. Nonetheless, underneath her wounding and often unpleasant manner, Shinku is kind and self-sacrificing. She's generous to a fault. She finds the physical and emotional cripple that is Suigintou and goes against her own interests in helping her. (Her current human medium keeps telling Shinku that she should be fighting the other dolls, not building up their self-esteem and teaching them how to walk.)
However Shinku's still a bigot. It's not her fault because that's simply the way she's been brainwashed by Father, but she thinks Suigintou is inherently inferior.
This is a simple story, but a strong one. It's a tragedy, albeit a quiet one where no one dies or even gets hurt. We already knew that Suigintou would become a villain, full of hatred and resentment. What we didn't know was how sad it would be to see the younger Suigintou so pathetically grateful, happy and emotionally dependent on Shinku. One day, she'll be strong. Here, she's a wreck. Ouch. This OVA's really, really good.
"Sarah, she's a good doll."