The Library of Souls is a device capable of copying any mortal being into a digital minion known as an "Ushabti". Created by the Ascended Ones, the Libraries were created as a means of carrying their vassals into their Afterlife: A digitally-simulated paradise.
After the downfall of their civilization, the few remaining Ascended Ones swore to destroy the remaining Libraries in order to ensure that no mortal would ever abuse its power. Despite this, a rouge Ascended One named Forneus gave a remaining Library to Dean Morris in order to test the potential of a Human Ushabti user.
In the game, the Library of Souls serves as your main menu, allowing you to view stats, change Ushabti, and save enemy data. It can also analyze and scan various objects and people, giving you a window into normally elusive minds.