The Ghost Rat AU is an Alternate Universe Fic by an anonymous author on the Watchmen Kinkmeme set in a fantasy universe, who also wrote the equally good High School A.U.. Both are long, well-written and well-researched stories that remain close to the original characterisation.
The story centers around three major characters - the fantasy versions of Rorschach, Daniel and Laurie who later form the central OT3 of the story. As in her High School A.U., most of the cast of Watchmen appears to some extent.
The series has (as of this writing) two major arcs. The first arc opens to Prince Daniel fleeing for his life after his Evil Uncle Moloch has usurped his father's throne. In the forests near his home he encounters the masked and taciturn Ghost Rat (guess who that is) and Laurie, the Princess of the Sunset Coast (because Everything's Better with Princesses) who is running away from an Arranged Marriage to the Emperor of the Eastern Isles who has no heart and cannot die. The second follows the OT3 plus a number of characters both original and otherwise on an archaeological expedition to find a dragon's bezoar to heal Daniel's poisoned mother.