At the end of the Showa era, the Media Betterment Act was enacted, beginning a country-wide hunt for all media that were deemed offensive. Witnessing the senseless censorship, libraries stood up against this law; the Library Defense Force (LDF) became the only entity capable of fighting off the Media Betterment Committee (MBC).

Tomboyish and avid reader Iku Kasahara is the newest member accepted into the Kanto branch of the LDF. Her love of reading has inspired her to join the force in more ways than one: she almost landed in trouble with the MBC five years prior when an unknown LDF agent came to her aid. Iku has since vowed to protect books just like that agent did, and—at just 22 years old—she has now become a promising talent among the new recruits.

Although Iku has achieved her dream of joining the LDF, she clashes with her superior Atsushi Doujou, a straight-laced instructor who seems to be particularly hard on her. For that reason, Iku is surprised to find out Doujou, among others, recommends her to be part of the Library Task Forces (LTF). Now part of an exclusive team, Iku must show her value as a member of LTF while executing her duties diligently.