In Genealogy of the Holy War, this tome is the Holy Weapon of Grannvale's House Freege, a faction that is lead by direct descendants of Tordo's lineage. The tome is first wielded by Reptor in Chapter 5, where he, alongside his fellow conspirator Langobalt, are manipulated by Arvis and Manfroy to combat Sigurd's troops. Reptor is slain in the conflict and the tome is passed down to his eldest son, Bloom.
The second generation of the game sees Bloom brandishing Mjölnir against Seliph's troops in Chapter 7 in the defense of Alster, before giving it to his daughter Ishtar in Chapter 8. Upon her defeat by Seliph's troops in this chapter, Julius enters the scene and warps her to safety. Ishtar later reappears with the tome in Chapter 10, where she engages in a game with Julius, with the victor being the first to slay any member of Seliph's army. She appears once again with Mjölnir in the Final chapter, where she puts up a valiant struggle against Seliph's troops, in honor of the members of her family who crumbled under their might.
According to Norse Mythology, Thor is the god of thunder, and is commonly depicted as a sentient being wielding the Mjölnir hammer in artwork pieces. Upon being thrown at a given target, the Mjölnir hammer is said to be able to return into the hands of its user.