Dantalian no Shoka (aka Bibliotheca Mystica de Dantalian, or The Mystical Archives of Dantalian) was a 12-episode, 1 OVA series by Gainax that aired through the summer of 2011. It is set in early 1920's England, right after the end of WWI, and follows a young man named Hugh Anthony Disward (or Huey to basically everyone) and a young girl named Dalian as they work together to round up magic tomes known as Phantom Books.
Though episodic in nature, the series is quite compelling as the pair deal with all manner of individuals in their efforts to round up the dangerous volumes before they wreak havoc in all sorts of ways. Dalian plays the tsundere role effectively and Huey has the patience of a saint, making them a superb comedy duo in their exploits. Though they could have gone the bumbling idiot route, instead Huey is an Air Force veteran ready and able to do battle with both human and demon, even without the help of magic. It makes for quite a thrill ride.
The art style in Dantalian is somewhat typical for an anime, but uses a lot of bright effects with a mostly dark pallet to make for a firmly gothic-lolita look. As if to confirm this, Gainax collaborated with fashion retailer Baby, The Stars Shine Bright and their child company Alice and the Pirates to design the costumes of the characters. Baby and Alice even went a step further by selling the fashions from the series, meaning that if one was so inclined (and had $1400 to spare at the time), one could dress as Dalian on a daily basis.
Making it even more rooted in its gothloli nature is the music. The opening, Cras Numquam Scire, is a gorgeous choral piece sung entirely in Latin, while the ending is a mysterious little song called yes, prisoner by a singer or band named maRIONnetTe (I've found no information on google, youtube, or wikipedia on either the singer or the backing band). Only adding to this is the ending itself, which is live-action, in black and white, and has nothing to do with the series save book pages falling from a tree and an obsession with keys. Beautiful as it is, it makes no sense, but at least it doesn't reflect poorly on the music, which is all soul-stirring.
With plenty of action, drama and mystery, this dark star of a series was quite the watch. It won't be everyone's bag, but it can appeal to a good chunk of fans if they're willing to give it a try. It's not sexual, it's not vulgar, and it's not very gorey, so outside of some possibly complex themes, concepts, or words, age won't be an issue here, either. Despite it looking like thorns on the outside, what's inside is actually an elegant rose.
Dantalian is available from Commie, Coalgirls, Deadfish, Horrible, M.3.3.W Subs, Zurako, Hatsuyuki Fansubs, Whine Subs, Yamayurikai and Nanaone (as a collaboration; German), Chinurarete Fansubs (German), Fairy Tale Fansub (Italian), Kanari Anime (Spanish), Urahara Shop (Hungarian), AnimeOu (Turkish), and Aria Chan Subs (OVA Only; Arabic). It was also released with english subs online by NicoNicoDouga and Crunchyroll.