The Book of Naga [ナーガ Nāga, lit. Naga, alternately translated Narga in Fire Emblem Treasure, and known as the Sacred Tome 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.
In Genealogy of the Holy War, this tome may only be wielded by characters who possess Naga holy blood, granting them the ability to call upon its sacred arcanes and summon the effigy of Naga into battle. This tome may only be obtained in the final chapter of the game, after Manfroy has been slain.
The Book of Naga is capable of negating the Loptyr tome's nefarious effect of halving enemy attack, essentially meaning that usage of said tome is crucial to defeating Julius with relative ease.