Finn Fish フィン・フィッシュ
Finn Fish is the angel, or semi-angel (jun-tenshi), who helps Maron detect demons and is also the one who transforms Maron into Kaito Jeanne.
(Source: Wikipedia)
Spoiler
It's revealed Finn had been manipulating Maron the whole time to gather chess pieces to deliver to the Devil. The former half-angel reveals herself as a fallen angel. She was in love with the Devil.
Same Voice Actors