Crom Cruach (クロウ・クルワッハ Kurou Kuruwaha) is a giant black dragon that appears in the final battle of Sin, Damnation and the Atonement Girl. It was unleashed by Avaritia as a last resort to eliminate all the Fragments along with their origin, Lieselotte Werckmeister.
Crom Cruach was released around the time of World War II in London. Considering the dragon a threat to humanity, the Holy Office of Index sent Saint Georgius, their most powerful saint, to London to defeat it once and for all. After a fierce battle, Georgius successfully defeated the dragon. However, he was cursed to bear the dragon's soul within his body for eternity, forcing him to even use the power of the Larvae to keep himself sane. While inside Georgius body's, the dragon continuously fed on his soul, straining the Saint even further. As a result, Georgius' magical capabilities greatly deteriorated, affecting him in future battles.
On November 2, 2009, the witch Lieselotte awakened and it was only a matter of time until she can break free from Georgius' seal. With no options left, Georgius' Black Knight incarnation, Avaritia, chose to unleash the dragon, hoping that it would destroy both Lieselotte and the Fragments of her VoidStone. The soul of the dragon consumed his body and invaded his mind, transforming him into a black dragon with a body of Larva origin. Most Georgius' sanity was eaten away, but the dragon, being a hybrid between the Black Knight and its former self was controlled by Avaritia's strong will. It encountered Shiori Momono and Kukuri Tachibana at the Akihara Bridge and had a fierce battle, with the dragon itself having the upper hand. However, the battle still ended with the Fragment girls' victory.
- Flight capability: despite its colossal size, the dragon can freely hover in the air, out of most opponents' reach.
- Fire blasts: the dragon can fire destructive fire blast, which will disintegrate everything it goes through, from its mouth.
- Immobilizing smoke: when dealing with multiple enemies, Crom Cruach releases some sort of black smoke that immobilizes its prey, allowing it to approach and kill the enemy with ease.
- Immense magical power: Crom Cruach is a dragon with almost unlimited magical power, which dwells in both its magic capabilities and physical strength. It has remained undefeated for a long period of time before Georgius came to kill it.
- Contract of the Rainbow (契約の虹 Keiyaku no Niji): after having merged with Avaritia, the dragon took both the power of the Larvae and Georgius, growing even more powerful than before it was sealed. It was capable of shooting Contract of the Rainbow whenever Shiori tried to charge a powerful spell.