Dorsal Dragons are so named because they have large fins along their backs that can be raised and lowered at will. They use these fins to regulate body temperature; they raise them to cool off when they become overheated. The bright colors on the fins double as a means of attracting mates.

Dragons are highly-intelligent reptilian creatures that—from a human perspective, at least—appear to live forever. Many different varieties of dragon exist, each with their own unique qualities, habitats, and behavior. Adolescence in dragons is usually marked by the growth of a hatchling’s wings, although not all breeds of dragons grow wings and some breeds have other traits that indicate the beginning of maturation. In Galsreim, dragons and humans coexist peacefully.

D'Agostino is a conscientious, austere, frail, and mild-mannered official's assistant from Cata Nyls, and her job involves doing arithmetic for the records and searching up documents for other people's research. She has a hard time telling a lie to protect herself, and lying on others' behalf involves a lot of preparation and psyching up on her part. She has a lot of loyal associates who admire, or are intrigued by, her earnestness and way with numbers, but she has only two or three friends. D'Agostino isn't very strong, and as adolescents, she and two of her cohorts, E.M. and Rabat, were accosted and nearly killed by a vicious rival of E.M.'s father. All three had lasting injuries—D'Agostino has a crooked, drooping left fin. While the other two vowed to become stronger and went on to learn many fighting techniques, D'Agostino instead chose to stay in the safety of her home where nobody could get her, and once she was considered an adult, she simply fled Cata Nyls.