Sara Tenneson, known as Sonoka Tokura (十倉 想乃香) in the Japanese version, is the librarian at the Kako Library. While she doesn't play a large role in the overall story, she does often help Ethan by looking up articles in the newspaper archives.
In some timelines, Chronos is not very successful. As a result, Olivia Eights is not employed there and does not meet Ben Fourier. In these timelines, Fourier develops a crush on Tenneson instead, leading him to checking out a large number of difficult books hoping to impress the librarian.