The elderly librarian ('Keeper of the Books') for the Sentinel Enclave just outside of Marcuria, Minstrum Yerin is a consummate bibliophile with a particular liking for Arcadian folktales. April Ryan meets him on the recommendation of Vestrum Tobias Grensret, when she is trying to find guidance on her journey.
Yerin spends most of his time absorbed in the business of the Enclave, and rarely leaves. He's kindly but slightly absent-minded. His first order of business is to ask April if she's seen a book he's looking for, then despairs of visitors to the library who don't sign out the books they borrow, before querying if April's one of the Dark People (whose library he greatly admires). However, his expertise is invaluable, especially when April's not sure what books she wants and can only ask about a topic. Yerin takes excellent care of the volumes, carrying them from the shelves to a reading table for April, then back again once she's finished. From his recommendations, April learns about the Alatien, the Draic Kin, and the Maerum, as well as gaining insights into Arcadia and the Northlands.
When April returns to the Enclave with the pieces of the Stone Disk, Yerin is happy to open the sluices for her when the Disk is cooling in the Enclave pool. April is concerned about how the elderly Minstrum will fare when the Tyren arrive, but Yerin reassures her that his magic is up to scratch, and that he can throw "a fair ball of fire" if necessary. However, if April asks after Vestrum Tobias, Yerin sadly tells her that he has been found dead in the Temple. Once he has opened the sluices, Yerin disappears into the Enclave and is not seen afterwards.
Minstrum Yerin is voiced by Peter Fernandez.