Pandora Hearts, Are You Alice? Recommendations
Alice in Wonderland references. The character designs are quite similar. The main characters - Oz and Alice (AYA?) are dragged into a abyss/world where they don't belong. They're personalities are quite similar but Alice seems a bit older than Oz. Gil/Mad-hatter has to protect Oz/Alice. Gil and Mad-hatter are very similar in character design and personality.
Both characters are dragged into a plot where they have to find something. Alice, a white rabbit and Oz, shards of memories.
Genres are also very similar.
Note: Alice is a guy.
In both the main protagonist is a blonde boy who is dragged to a dangerous world where supernatural creatures exist. Also many similarities in the characters situations or personalities: a noble girl who befriends the protagonist, a guy with lack of memories, a tormented cat that is related to Alice's past, a mysterious important character that appears in visions/dreams, a girl that hates and blames someone for a certain situation, a boy that did everything for the person he cared for, even if that costs the life of others, a cruel character that reigns in the wonderland. If you liked one, you certainly like the
Mystery mangas with Alice in Wonderland's references. The main boy/man is dragged to a world full of mysteries where he has to search for answers and is often caught in other characters' memories.
Both of them are quasi-homages to Lewis Carroll's "Alice's Adventures in Wonderland" and both have the same feel to them--somewhat funny comedy mixed with twisted storytelling and artwork. Although neither is an adult manga (in the hentai sense), they take even darker journeys down the rabbit hole than Carroll's story does. Plus, anyone who wants beautiful bishounen and pretty artwork should check these out. Despite the fact that neither manga is identical to the other, the tones are similar enough that this is an easy recommendation.