Ms.Librarian

A female ghost who's always in the library.

She's lingered in this world for quite some time, which has made her very knowledgeable about the dead.
Her expertise often helps Shiori and the protagonist.

Unlike Shiori and the other ghosts, she still has memories from when she was alive.
She seems to have some major regret binding her in the library, but she rarely talks about herself

Edited from Steam