High school student Maron Kusakabe has a secret: she's Phantom Thief Jeanne. She sneaks into private art collections to steal paintings in which demons reside. Jeanne's task is to seal the demons before they can devour human hearts. So far she's been able to evade the police on her midnight outings, but now another thief has come onto the scene - Phantom Thief Sinbad - and he's trying to take the paintings before she does! The Demon Lord takes Chiaki hostage and challenges Maron to a battle of life or death. But rather than fight her himself, the Demon Lord has selected another to be his champion. Can Maron find the strength to fight alone against her only remaining ally?