From J-Novel Club:
Archdemon Zagan hires his unsavory friend, the sorcerer known as Purgatory Barbatos, to guard Archangel Chastille Lillqvist from the shadows. Barbatos takes to watching over the girl. This means watching her constantly screw things up, trust people she shouldn’t, and inevitably bawl her eyes out. But something about Chastille and her waterworks may just have…