Mushikaburi-hime

Elianna Bernstein comes from a family famous for loving books, and she would rather spend an entire day in a library than attend parties or political gatherings. That makes Crown Prince Christopher's offer easy to accept: become his fiancée in name and perform the necessary public duties, and in return she may freely use the royal archives and read to her heart's content.

Four years pass with Elianna assuming the arrangement is still only a convenient bargain, until she sees Christopher growing close to another girl and hears people expecting a change of fiancée. For the first time she realizes that losing him hurts more than losing access to books, and that the prince may never have considered their engagement a political performance in the first place.