In 1989, the Japanese government passed the Media Betterment Act to protect the youth from being influenced by negative materials in the media. To counter this, local governments throughout the country establish "Library Defense Forces" to prevent Media Betterment Act agents from infringing on people's rights to access media deemed as banned material. A civilian, Iku Kasahara, had been accosted by an MBA agent who attempts to take away a banned book from her, but is saved by an LDF agent. Inspired, Kasahara decides to join in the Library Defense Force.