The Dead Boy Detectives (2005) by Jill Thompson: The two, um, dead boys who would become The Dead Boy Detectives are Charles Rowland and Edwin Paine, forever 13 and 12, respectively, the former dying in 1990 and the latter in 1916, both at the same horrible boys' school in England. They managed to avoid being collected by Death in the pages of Neil Gaiman's Sandman and now solve crimes whenever they can.
Here, they find themselves in a B&W, manga-influenced adventure written and illustrated by Jill Thompson. They go undercover at the International Academy in Chicago, a girls' school for the wealthy. Various shenanigans ensue while things are kept light. It's fun and frothy, which is not a description one would usually attach to the Sandman source text. Recommended.