Serenity loses her twin brother and her parents at a young age after touching a cursed diary. In order to find out what happened to her brother, who she believes is still alive, she sets off on a journey with a devil who claims to be Satan's son, even though he doesn't resemble him in anyway. Together they work in searching for her brother, all while befriending other creatures and trying to keep the weakening bridge between Hell and Earth from breaking.