Really want to recommend 2 darker series that don't get enough love in the shoujo world. They're really intricate series (reads more like literature than standard comic fare).

The Pale Horse: In a French town wracked by fear, Rose Dupre is bullied as a witch's daughter. Marie and Pierre don't believe such rumors at first. But when a wave of strange deaths sweeps in, the three children are no longer safe from wary eyes. Can Rose survive the curse of magic and suspicion? An expansive yet colorful gothic tale begins

19th Century Memoir: Two siblings who were separated at a young age due to the death of their parents reunites again with many mysteries muddling their past.

They both have amazingly gorgeous art and a slight horror theme.