The Book of Naga [ナーガ Nāga, lit. Naga, alternately translated Narga in Fire Emblem Treasure, and known as the Holy Book Naga (聖書ナーガ Seisho Nāga) in the Japanese version of Awakening) is one of twelve holy weapons from Fire Emblem: Genealogy of the Holy War. The Book of Naga is the tome that was originally wielded by the Crusader Heim, bestowed upon him by the Divine DragonNaga during the Miracle of Darna.
In Genealogy of the Holy War, this tome may only be wielded by characters who possess major Naga holy blood. In theory, both Deirdre and her daughter Julia are able to wield the tome, but only the latter will have access to it.
The Book of Naga is capable of negating the Loptyr tome's effect of halving enemy attack, essentially meaning that its usage is crucial to defeating Julius.
The Book of Naga is first mentioned in Genealogy of the Holy War in the Final Chapter, after the fall of Velthomer to Seliph's army. Lewyn reveals that Arvis had, prior to the Final Chapter's events, removed it from the Royal Palace at Belhalla and hid it within Velthomer Castle. The key to the chest holding the tome is revealed to be Deirdre's Circlet, which is in the possession of Julia. Julia later retrieves the Book of Naga and uses it to lead the army to a resounding victory over Julius, ending the last holy war.