What the title says...
As far as I know AU stands for alternative universe...
Dramatical Murder AU is an Alternate Universe with The dramarical murder characters is kinda like changing the story. SAy like a story where everyone is in high school, Mink's is the teacher, Noiz is a science freak, Koujaku is on the football team, Clear helps with the school garden (and he's human) and Aoba is the cheerleader for Koujaku's team. See? stuff like that? I hope it helped?