The Klara Libri is the oldest artifact in the history of Aernas. It is a sacred tome containing all the secrets of the world, including all information about the gods, the Creator God and the demonic tribes.
Kassias Grandiel holds a replica of the Klara Libri, though it is said to be significantly less powerful than the original. However, it was still powerful enough to defeat Ashtaroth in his god-like form and seal him away.
The tome was first discovered by the ambitious Baldinar, without anyone's notice. He went crazy, hatching a plan to become the new Creator God and so much more in order to obtain absolute control over the powers of evil and good.
He went on to study the demons that had been trapped in Aernas and collected the Demonic Essence, the source of the power of darkness. To act as the source of the power of good, he decided to use the power of the gods which still lay inside the Aernas Hammer. Following the instructions of the Klara Libri, he used this power to create the Soul Stone, a crystal containing the power of the deities. His plan was to unite the Soul Stone, the Aernas Hammer, and the Demonic Essence, and thus obtain the ultimate weapon to become the new Creator. This ambition led to the tragedy of Kounat.
Baldinar tried to use the Soul Stone to power the Aernas Hammer. His plan was to eliminate all obstacles that could stand in his way and destroy the Highlanders, the champions of the gods who had participated in the War. However, the only people of Kounat that were able to control the energies of Soul Stone were members of the royal family, who were able to withstand the "Geas" that would be imposed upon them by the gods.
Due to the corrupted Baldinar, the Aernas Hammer, which was already unstable, went berserk. The Prime Minister lost control of the weapon, and it released all its uncontrollable power over a gigantic explosion. From the palace, the royal family could only watch helplessly as the devastating power surge that consumed their kingdom and drew closer and closer.
Kassias Grandiel later obtains the Klara Libri's clone, though how he acquires it is never mentioned.
In present day, Kassias Grandiel utilizes the power of the Klara Libri's clone to forcibly warp the entire Grand Chase into his Labyrinth and combat them as an attempt to train them to defeat Ashtaroth.
Later, Kassias Grandiel again employs the Klara Libri's clone to warp the Grand Chase into the Underworld's Monster Train 301 as an attempt to retrieve Harpe Noir's soul. Ashtaroth comments of Grandiel holding the clone.
Finally, Kounat's Collapse, Kassias Grandiel uses the Klara Libri's clone to defeat Graham's Relics and Ashtaroth after he transforms into a god; afterwards, he uses it to seal Ashtaroth and the Aernas Hammer as well as himself in the Wizard's Labyrinth. Void then erases Mari's memories of the Klara Libri to ease her suffering, and then takes the tome.
- The Klara Libri is also known as the Claire Bible and the Bible of Revelations.
- Grandiel's copy of the Klara Libri has a blue and white cover, as compared to the brown and gold cover of the original.
- Rune Caster's Grimoire takes the appearance of a deep blue-colored Klara Libri with the cover's corners and the insides also blue rather than gold and brown respectively during her Buster Lv 2 and Core Break Specials. This suggests that Mari's Grimoire is actually another clone of the Klara Libri or is the original one recolored to match her color scheme.