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.   

 ~!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.!~    (Source: Wikipedia)

A normal looking high school girl on the outside, Kusakabe Maron is actually the reincarnation of Jeanne d' Arc. With the help of the angel, Fin Fish, Maron works as the thief Jeanne at night to seal the demons that reside in pieces of artwork, preying upon the weak hearts of the owners. She is branded as a thief due to the fact that the artworks disappear after she seals the demons. One day, a new neighbor and classmate appears, as well as a rival in her night job, the thief Sinbad. With her own best friend being the detective's daughter, out to capture her and the appearance of her new rival, Maron's work is anything but easy.

__[Profile](https://www.aoni.co.jp/search/nishihara-kumiko.html)__

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 Sinbad—and he’s trying to take the paintings before she does!
 
(Source: Viz Media)
 
 
Notes: 
- Includes bonus stories "Miyako☆Catharsis", "Instant?! Access Legend★", "Let's Go, Silk Road ★"
 
- "The Memory of the Fish, The Snow Crystals of the Moon" 1-2 and "I Will Be Your Happiness" are not included as they are only released in the Bunko edition (but not in the initial release of the manga)