Library of Ruina takes place in a dystopian world known as the City, which is made of twenty-six districts. The City is governed by the a reclusive organization known as the Head, while the Nests are run by Wings, mega-corporations that harness powerful technologies known as Singularities. The backstreets are crime-riddled areas controlled by various crime syndicates. Outside of the City are the Outskirts, a barren hell-like wasteland, and the Ruins, eldritch landscapes beyond the Outskirts.
Throughout the City, there are many offices run by Fixers, mercenaries regulated by the government. Each Fixer is assigned a grade based on their skill and experience.
Following the events of Lobotomy Corporation, the AI Angela creates the Library out of the light produced by Lobotomy Corporation's Seed of Light, creating an incident known as the "White Nights and Dark Days". This incident and its aftermath, mainly the Distortion phenomenon, directly influence the game's plot.
Before Angela opens the Library, a low-level Fixer named Roland appears in it and is forcefully recruited by Angela to be her guide to the City. Angela wishes to find the "one perfect book" that contains the answers she desires and turns her human. She sends out Invitations and has Roland and her other librarians battle the guests. If the guests win, they are allowed to take books from the library; if they lose, they become a book themselves.
Story
The player follows Angela's journey toward the "one perfect book" in the Library from the view of Roland, a Fixer who becomes her servant after trespassing into the Library uninvited.
The story is broken up into various chapters. As Roland's past is gradually shed light on and Angela comes closer to becoming human, the Library becomes an ever-growing threat to the City, urging City Associations to take action. A mysterious Fixer known as Argalia recruits various characters for an unknown cause, culminating in them breaking into the Library, scattering to the ten floors to claim the Light for their greatest performance that will overturn the City. The Library ultimately emerges victorious after a hard-fought battle.
Just as Angela finally gains a human body, Roland betrays Angela and reveals his true motive for coming to the Library: to make her suffer as revenge for her actions instigating the Distortion phenomenon and indirectly causing the death of his wife. Roland ultimately fails to defeat the Library and pleads for Angela to kill him, or he will kill her if she falters.
If all of Angela's Floor realizations have not been completed, she will kill Roland and the Librarians and obtain the one true book. Angela, burdened by the guilt of killing her friends and the city folk, continues her aimless destruction for years before letting a nameless follower end her life. If all of Roland's Floor realizations have not been completed, Roland will swiftly behead Angela before returning to the City, his life spiraling into drug abuse and wanton slaughter before eventually dying meaninglessly in a gutter.
If all Floor realizations have been completed and Angela and Roland choose to forgive each other, Angela will release the culminated Light and resurrect all lives the Library has taken, kickstarting the Kether floor realization facing against Carmen, founder of Lobotomy Corporation's Seed of Light and actual mastermind behind the Distortion phenomenon. Meanwhile, Roland and the Library fight back the returned Reverberation Ensemble, now empowered by the Light, for 7 days; Roland saves Angela from dissipating inside the Light and kills Argalia for good.
The Library soon receives the arrival of the Head, who aims to expel the Library from the City and to exterminate Angela. Facing great retaliation from Roland and fellow librarians Gebura and Binah, the Head agents decide to instead stick to their main plan and expel the Library into the Outskirts. As they step outside of the Library, Angela and Roland reconcile as they decide to reopen the location under a new direction.
