It's difficult to explain because the anime, especially the manga, it's too complicated and intricate, full of mistery, but it's really cool ^ ^ It's a psycological, mysterios, of action and a little bit romantic shonen. The anime has 25 episodes, but the last 3 are completely invented and the mistery aren't solved, so I advice you to read the manga. A short plot that I find in this site (you can read the manga here)
link
From Yen Press: The air of celebration surrounding fifteen-year-old Oz Vessalius’s coming-of-age ceremony quickly turns to horror when he is condemned for a sin about which he knows nothing. He is thrown into an eternal prison known as the Abyss, from which there is no escape. There, he meets a young girl named Alice, who is not what she seems. Now that the relentless cogs of fate have begun to turn, will they lead only to crushing despair for Oz, or is there some shred of hope for him to grasp on to?
Now I explain, the Abyss is a different dimension like hell and purgatory, time is distorted,but if you be able to escape you cannot return to your time. Alice is a chain, the inhabitants of the Abyss, Oz and Alice make a contract for escape because Alice wants to find her lost memories. Back in the real world they begin to search, but there will be many other mysteries. Everyone search something because they want to know who they really are (for Oz and Alice) Oz also want to know what is his sin, in conclusion everyone search a hidden truth, so begins this incredible research, which seems endless. This manga is inspired by Alice in Wonderland, but only for something. I hope to has been helpful and that you will read this wonderful manga ^ ^ and watch the anime too ^ ^
This is an image of the main characters ^ ^
Oz is the blond boy, Alice is the girl with violet eyes (they are the main characters) then Gilbert (dark hair) Sharon and Break (secondary characters)
Bye ^ ^