Eighteen months after the formation of the Library Defense Force, the battle against the Media Betterment Act has reached a critical turning point. In a near-future Japan where government censorship has been brutally enforced through armed Betterment Squads that confiscate and destroy any deemed harmful material, the Library Defense Force stands as the last line of defense for intellectual freedom. The story follows Iku Kasahara, now a fully-fledged member of the Task Force, the elite combat unit of the Kantō Library Defense Force. She continues to serve under the harsh but dedicated supervision of her commanding officer, Atsushi Dojo, the man she secretly admires and who once inspired her to join the force years ago when he retrieved a book that had been targeted for censorship.

The unit is assigned what appears to be a straightforward but highly symbolic mission: to guard a public exhibition at an arts festival showcasing The Handbook of Library Law, the only remaining copy of a book considered the very symbol of freedom of expression. Protecting this irreplaceable artifact should be a point of pride for the Task Force, but the mission quickly reveals itself to be an elaborate trap. The architect of this plot is Satoshi Tezuka, the brilliant but disillusioned older brother of Iku's colleague and rival, Hikaru Tezuka. Satoshi believes that the constant stalemate with the censorship forces has rendered the Library Defense Force obsolete and aims to destroy the Task Force entirely, believing that eliminating them will help correct a society he sees as morally twisted.

As the Betterment Squads launch a massive and well-coordinated assault on the exhibition, the Task Force finds itself in the fight of its lives, outnumbered and under siege. The narrative arc focuses on the group's desperate struggle to survive, protect the book, and expose Satoshi's scheme. Amidst the intense action, personal relationships are pushed to a breaking point, particularly the unspoken romantic tension between Iku and Dojo, which faces its ultimate test as they confront mortal danger together. The film also deepens the internal conflicts within the unit as they question the effectiveness of their cause when faced with such overwhelming opposition and betrayal from within their own ranks.