Rosina is a character that appears in the Ascendance of a Bookworm series.
Along with Vilma, Rosina was a former attendant of Miss Christine when she was a priestess in the Temple. After Miss Christine leaves, Rosina is assigned to Myne by Ferdinand to teach her music and how to act like a proper lady.
She has better luck with the music lessons. Mynes (Urano) knowledge from earth music comes in handy. She teaches Rosina music from quite a few Anime shows she used to watch on earth and also gives music sheets (with the help of Ferdinand who transposes the music for her) for Rosina coming of age present.
Rosina becomes Rozemynes personal musician when Myne is becomes a noble. Which she is over joyed at and happily accepts.