Finn Fish is the small female semi-angel who helps Maron detect demons and gave her the power to transform into Phantom Thief Jeanne. When Maron first saw her, she thought Finn was a fairy. Maron learns that Finn is actually the devil's advocate. Her real job is to hurt Joan of Arc's reincarnation, Maron Kusakabe. If she fills Maron's heart with evil, she will get hurt, and her powers will disappear. The Devil needed God's power — humans' beauty and purity that were in their hearts.